ENOUGH has, I trust, been stated in the preceding chapter, to show the paramount importance of appealing to organic remains, in illustration of that branch of physico-theology with which we are at present occupied.

The structure of the greater number, even of the earliest fossil Mammalia, differs in so few essential points from that of the living representatives of their respective Orders, that I forbear to enter on details which would indeed abound with evidences of creative design, but would offer little that is not equally discoverable in the anatomy of existing species. I shall, therefore, limit my observations to two extinct genera, which are perhaps the most remarkable of all fossil Mammalia, for size and unexampled peculiarities of anatomical construction the first of these, the Dinotherium, having been the largest of terrestrial Mammalia; and the second, the Megatherium, presenting greater deviations from

[136 FOSSIL MAMMALIA.] ordinary animal forms, than occur in any other species, either of recent or fossil quadrupeds.
It has been already stated, in our account of the Mammalia of the Miocene period of the tertiary series, that the most abundant remains of the Dinotherium are found at Epplesheim, in the province of Hesse Darmstadt, and are described, in a work now in process of publication, by Professor Kaup. Fragments of the same genus are mentioned by Cuvier, as occurring in several parts of France, and in Bavaria and Austria.

The form of the molar teeth of the Dinotherium (Pl. 2, C. Fig. 3), so nearly resembles that of the Tapirs, that Cuvier at first referred them to a gigantic species of this genus. Professor Kaup has since placed this animal in the new genus Dinotherium, holding an intermediate place between the Tapir and the Mastodon, and supplying another important extinct link in the great family of Pachydermata. The largest species of this genus, D. Giganteum, is calculated, both by Cuvier and Kaup, to have attained the extraordinary length of eighteen feet. The most remarkable bone of the body yet found is the shoulder-blade, the form of which more nearly resembles that of a Mole than of any other animal, and seems to indicate a peculiar adaptation of the fore leg to the purposes of digging, an indication which is

[137 DINOTHERIUM .] corroborated by the remarkable structure of the lower jaw.

The lower jaws of two species of Dinotherium, figured in Plate 2. C. Figs. l. 2. exhibit peculiarities in the disposition of the tusks, such as are found in no other living or fossil animal.

The form of the molar teeth, Pl. 2. C. Fig. 3, approaches, as we have stated, most nearly to that of the molar teeth in Tapirs; but a remarkable deviation from the character of Tapirs, as well as of every other quadruped, consists in the presence of two enormous tusks, placed at the anterior extremity of the lower jaw, and curved downwards, like the tusks in the upper jaw of the Walrus. (Pl. 2. C. l. 2.)

I shall confine my present remarks to this peculiarity in the position of the tusks, and endeavour to show how far these organs illustrate the habits of the extinct animals in which they are found. It is mechanically impossible that a lower jaw, nearly four feet long, loaded with such heavy tusks at its extremity, could have been otherwise than cumbrous aud inconvenient to a quadruped living on dry land. No such disadvantage would have attended this structure in a large animal destined to live in water; and the aquatic habits of the family of Tapirs, to which the Dinotherium was most nearly allied, render it probable that, like them, it was an inhabitant of fresh-water lakes and

[138 FOSSIL MAMMALIA.] rivers. To an animal of such habits, the weight of the tusks sustained in water would have been no source of inconvenience; and, if we suppose them to have been employed, as instruments for raking and grubbing up by the roots large aquatic vegetables from the bottom, they would, under such service, combine the mechanical powers of the pick-axe with those of the horse-harrow of modern husbandry. The weight of the head, placed above these downward tusks, would add to their efficiency for the service here supposed, as the power of the harrow is increased by being loaded with weights.

The tusks of the Dinotherium may also have been applied with mechanical advantage to hook on the head of the animal to the bank, with the nostrils sustained above the water, so as to breathe securely during sleep, whilst the body remained floating, at perfect ease, beneath the surface: the animal might thus repose, moored to the margin of a lake or river, without the slightest muscular exertion, the weight of the head and body tending to fix and keep the tusks fast anchored in the substance of the bank; as the weight of the body of a sleep ing bird keeps the claws clasped firmly around its perch. These tusks might have been further used, like those in the upper jaw of the Walrus, to assist in dragging the body out of the water; and also as formidable instruments of defence.

[139 MEGATHERIUM.] The structure of the scapula, already noticed, seems to show that the fore leg was adapted to co-operate with the tusks and teeth, in digging and separating large vegetables from the bottom. The great length attributed to the body, would have been no way inconvenient to an animal living in the water, but attended with much mechanical disadvantage to so weighty a quadruped upon land. In all these characters of a gigantic, herbivorous, aquatic quadruped, we recognize adaptations to the lacustrine condition of the earth, during that portion of the tertiary periods, to which the existence of these seemingly anomalous creatures appears to have been limited.

As it will be quite impossible, in the present Treatise, to give particular descriptions of the structure, even of a few of the fossil Mammalia, which have been, as it were, restored again to life by the genius and industry of Cuvier; I shall endeavour to illustrate, by the details of a single species, the method of analytical investigation, that has been applied by that great philosopher to the anatomy both of fossil and recent animals.

The result of his researches, as recorded in the Ossemens Fossiles, has been to show that all

[140 FOSSIL MAMMALIA.] fossil quadrupeds, however differing in generic, or specific details, are uniformly constructed on the same general plan, and systematic basis of organization as living species; and that throughout the various adaptations of a common type to peculiar functions, under different conditions of the earth, there prevails such universal conformity of design, that we cannot rise from the perusal of these inestimable volumes, without a strong conviction of the agency of one vast and mighty Intelligence, ever directing the entire fabric, both of past and present systems of creation.

Nothing can exceed the accuracy of the severe and logical demonstrations, that fill these volumes with proofs of wise design, in the constant relation of the parts of animals to one another, and to the general functions of the whole body. Nothing can surpass the perfection of his reasoning, in pointing out the beautiful contrivances, which are provided in almost endless variety, to fit every living creature to its own peculiar state and mode of life. His illustration of the curious conditions, and concurrent compensations that are found in the living Elephants, apply equally to the extinct fossil species of the same genus; and similar exemplifications may be extended from the living to the extinct species of other genera, e. g. Rhinoceros, Hippopotamus, Horse, Ox, Deer, Tiger, Hyæna, Wolf, &c. that are usually associated with the Elephant in a fossil state.

[141 MEGATHERIUM.] The animal I shall select for my present purpose is that most extraordinary fossil creature, the Megatherium, (see Pl. 5), an animal, in some parts of its organization, nearly allied to the Sloth, and, like the Sloth, presenting an apparent monstrosity of external form, accompanied by many strange peculiarities of internal structure, which have hitherto been but little understood .

The Sloths have afforded a remarkable exception to the conclusions which naturalists have usually drawn, from their study of the organic structure and mechanism of other animals. The adaptation of each part of the body of the Elephant, to produce extraordinary strength, and of every member of the Deer and Antelope to give agility and speed, are too obvious to have escaped the attention of any scientific observer; but, it has been the constant practice of naturalists, to follow Buffon in misrepresenting the Sloths, as the most imperfectly constructed among all the members of the animal kingdom, as creatures incapable of enjoyment, and formed only for misery.

The Sloth does, indeed, afford the greatest deviations from the ordinary structure of living quadrupeds; and these have been erroueously considered as imperfections in its organization, without any compensating advantage. I have elsewhere* attempted to show that these anomalous

* Linnean Transactions, Vol. XVII. Part 1 .

[142  FOSSIL MAMMALIA.] conditions are so far from being defects, or sources of inconvenience in the Sloth, that they afford striking illustrations of the varied contrivances, whereby the structure of every creature is harmoniously adapted to the state in which it was destined to live. The peculiarities of the Sloth, that render its movements so awkward on the earth, are fitted with much advantage to its destined office of living entirely upon trees, and feeding upon their leaves: so also, if we consider the Megatherium with a view to its province of digging and feeding upon roots, we shall, in this habit, discover the explanation of its unusual structure, and apparently incongruous proportions; and find, in every organ, a relation of obvious convenience, and of adaptation to the office it had to discharge.*

It will be my present object to enter into such a minute investigation of some of the more re markable parts of this animal, viewing them with a constant reference to a peculiar mode of life, as may lead to the recognition of a system of well

* The remains of the Megatherium have been found chiefly in the southern regions of America, and most abundantly in Paraguay; it appears also to have extended on the north of the equator as far as the United States. We have, for some time, possessed detailed descriptions of this animal by Cuvier, Oss. Foss. vol. 5. and a series of large engravings, by Pander and D'Alton, taken from a nearly perfect skeleton, sent in 1789 from Buenos Ayres to Madrid. Dr. Mitchell and Mr. Cooper have described, in the Annals of the Lyceum of Nat. Hist. of New York, May, 1824, some teeth and bones found in the marshes of

[143 MEGATHERIUM.] connected contrivances, in the mechanism of a creature apparently the most monstrous, and seeming to present the most ill-assorted proportions, that occur throughout the entire range of the animal kingdom.

We have here before us a gigantic quadruped, (see Pl. 5, Fig. 1), which at first sight appears not only ill-proportioned as a whole, but whose members also seem incongruous, and clumsy, if considered with a view to the functions and corresponding limbs of ordinary quadrupeds: let us only examine them with the aid of that clue, which is our best and essential guide in every investigation of the mechanism of the animal frame; let us first infer from the total composition and capabilities of the machinery, what was the general nature of the work it was destined to perform; and from the character of the most important parts, namely, the feet and teeth, make ourselves acquainted with the food these organs were adapted to procure and masticate; and we shall find every other member of the body acting

the Isle of Skiddaway, on the coast of Georgia, which correspond with the skeleton at Madrid. Cuvier, Vol. V. part 2, p. 519. — In the year 1832, many parts of another skeleton were brought to England by Woodbine Parish, esq. from the bed of the river Salado, near Buenos Ayres: these are placed in the museum of the Royal College of Surgeons in London, and will be described in the Trans. Geol. Soc. Lond. Vol. III. N. S. Part 3, by my friend Mr. Clift, a gentleman from whose great anatomical knowledge, I have derived most important aid, in my investigation of  this animal.

[144 FOSSIL MAMMALIA.] in harmonious subordination to this chief purpose in the animal economy.

In the case of ordinary animals, the passage from one form to another is so gradual, and the functions of one species receive such ample and obvious illustrations from those of the species adjacent to it, that we are rarely at a loss, to see the final cause of almost every arrangement that is presented to the anatomist. This is more especially the case with respect to the skeleton, which forms the foundation of all the other mechanisms within the body, and is of the highest importance in the history of fossil animals, of which we rarely find any other remains besides the bones, and teeth, and the scaly or osseous integuments. I select the Megatherium, because it affords an example of most extraordinary deviations, and of egregious apparent monstrosity; viz, the case of a gigantic animal exceeding the largest Rhinoceros in bulk, and to which the nearest approximations that occur in the living world, are found in the not less anomalous genera of Sloth, Armadillo, and Chlamyphorus; the former adapted to the peculiar habit of residing upon trees; the two latter constructed with unusual adaptations to the habit of burrowing in search of their food and shelter in sand; and all limited in their geographical distribution, nearly to the same regions of America that were once the residence of the Megatherium .

[145 MEGATHERIUM.] I shall not here enter on the unsettled questions as to the precise age of the deposits in which the Megatherium is found, or the causes by which it has been extirpated; my object is to show that the apparent incongruities of all its parts, are in reality systems of wise and well contrived adaptation to a peculiar mode of life. I proceed therefore to consider, in the order in which they are described by Cuvier, the most important organs of the Megatherium, beginning with the head, and from thence advancing to the trunk and extremities.

The bones of the head (Pl. 5, Fig. I. a.) most nearly resemble those of a Sloth. The long arid broad bone, (b,) descending the cheek from the zygornatic arch, connects it more nearly with the Ai than with any other animal: this extraordinary bone must have been auxiliary to the power of muscles, acting with more than usual advantage, in giving motion to the lowerjaw (d).

The anterior part of the muzzle (c) is so strong and substantial, and so perforated with holes for the passage of nerves and vessels, that we may be sure it supported some organ of considerable size: a long trunk was needless to an animal possessing so long a neck; the organ was probably a snout, something like that of

[146 FOSSIL MAMMALIA.] the Tapir, sufficiently elongated to gather up roots from the ground. The septum of the nostrils also being strong and bony, gives further indication of the presence of a powerful organ appended to the nose; such an apparatus would have afforded compensation for the absence of incisor teeth and tusks. Having no incisors, the Megatherium could not have lived on grass. The structure of the molar teeth (Pl. 5, Fig. 6-11, and Pl. 6, No. 1), shows that it was not carnivorous.

The composition of a single molar tooth resembles that of one, of the many denticules, that are united in the compound molar of the Elephant; and affords an admirable exemplification of the method employed by Nature, whereby three substances, of unequal density viz. ivory, enamel, and crusta petrosa, or cementum, are united in the construction of the teeth of graminivorous animals. The teeth are about seven inches long, and nearly of a prismatic form (Pl. 5, Fig. 7-8). The grinding surfaces (Pl. 5, Fig. 9. a. b. c. and Pl. 6, Z. a. b. c.) exhibit a peculiar and beautiful contrivance for maintaining two cutting wedge-shaped salient edges, in good working condition during the whole existence of the tooth; being, as I before stated, a modification of the contrivance employed in the molars of the Elephant, and other herbivora. The

[147 MEGATHERIUM.] same principle is applied by tool-makers for the purpose of maintaining a sharp edge in axes, scythes, bill-hooks, &c. An axe, or bill-hook, is not made entirely of steel, but of one thin plate of steel, inserted between two plates of softer iron, and so enclosed that the steel projects beyond the iron, along the entire line of the cutting edge of the instrument. A double advantage results from this contrivance; first, the instrument is less liable to fracture than if it were entirely made of the more brittle material of steel; and secondly, the cutting edge is more easily kept sharp by grinding down a portion of exterior soft iron, than if the entire mass were of hard steel. By a similar contrivance, two cutting edges are produced on the crown of the molar teeth of the Megatherium. (See Pl. 6, W. X. Y. Z. and Pl. 5, Figs. 6-10.)*

* The outside of the tooth, like that of an axe, is made of a comparatively soft material, viz, the crusta petrosa, (a a), inclosing a plate of enamel, (b b), which is the hardest substance, or steel of the tooth. This enamel passes twice across the grinding surface, (z), and forms the cutting edges of two parallel wedges, Y. b. b.: a longitudinal section of these wedges is seen, Pl. 6, v. w. x. y. Within the enamel, (b b), is a central mass of ivory, (c), which, like the external crust, (a) is softer than the enamel. A tooth, thus constructed of materials of unequal density, would have its softer parts, (a c), worn down more readily than the harder plates of enamel, (b b).

We find a further nicety of mechanical contrivance, for producing and maintaining two transverse wedges upon the surface

[148 FOSSIL MAMMALIA.] Pl. 6, W. X. represents the manner in which each lower tooth was opposed to the tooth above it, so that the hard enamel of the one should come in contact only with the softer materials of the other; viz. the edges of the plates of enamel, (b) rubbing upon the ivory, (c); and the enamel, (b'), upon thE crusta petrosa, (a), of the two teeth opposite to it. Hence the act of mastication formed and perpetually maintained a series of wedges, locking into each other like the alternate ridges on the rollers of a crushing-mill; and the mouth of the Megatherium became an engine of prodigious power, in which thirty-two such wedges formed the grinding surfaces of sixteen molar teeth ; each from seven to nine inches long, and having the greater part of this length fixed firmly in a socket of great depth.

As the surfaces of these teeth must have worn away with much rapidity, a provision, unusual in molar teeth, and similar to that in the incisor teeth

of each tooth, in the relative adjustment of the thickness, of the lateral and transverse portions of the plate of enamel, which is interposed between the external crust, (a), and the central ivory, (c). Had this enamel been of uniform thickness all round the central ivory, the tooth would have worn down equally to a horizontal surface. In the crown of the tooth, Pl. 6, Z. the plate of enamel is seen to be thin on the two sides of the tooth, whilst the transverse portions of the same plate, (b. b.) are comparatively thick and strong. Hence the weaker lateral portions of thin enamel wear away more rapidly, than the thicker and stronger transverse portions, (b b), and do not prevent the excavation of the furrow across the surface of the ivory, c.

[149 MEGATHERIUM.] of the Beaver and other Rodentia,* supplied the loss that was continually going on at the crown, by the constant addition of new matter at the root, which for this purpose remained hollow, and filled with pulp during the whole life of the animal.

It is scarcely possible to find any apparatus in the mechanism of dentition, which constitutes a more powerful engine for masticating roots, than was formed by these teeth of the Megatherium; accompanied also by a property, which is the perfection of all machinery, namely, that of maintaining itself perpetually in perfect order, by the act of performing its work.

The lower jaw (Pl. 5, l. d.) is very large and weighty in proportion to the rest of the head; the object of this size being to afford deep sockets

* The incisors of the Beaver, and other Rodentia, and tusks of the Hog and Hippopotamus, which require only an external cutting edge, and not a grinding surface, are constructed on the same principle as the cutting edge of a chisel or an adze; viz, a plate of hard enamel is applied to the outer surface only, of the ivory of these teeth, and in the same manner as the outer cutting edge of the chisel and adze is faced with a plate of steel, welded against an inner plate of softer iron. A tooth thus constructed maintains its cutting edge of enamel continually sharp, by the act of working against the similarly constructed extremity of the tooth opposed to it.

Pl. 5, Fig. I I, iepresents the section of the cavity containing this pulp.

[150 FOSSIL MAMMALIA.] for the continual growth and firm fixture of the long and vertical molar teeth; the extraordinary and strong process (b) descending from the zygomatic arch in the Megatherium, as well as in the Sloths, seems intended to support the unusual weight of the lower jaw consequent upon the peculiar form of the molar teeth.

The vertebræ of the neck, though strong, are small in comparison with those towards the opposite extremity of the body;  being duly proportioned to the size of a head, comparatively light, and without tusks. The dorsal portion of the vertebral column is of moderate size, but there is an enlargement of the vertebræ of the loins, corresponding with the extraordinary bulk of the pelvis and hind-legs; the summits of the spinous processes, (e,) are flattened like those in the Armadillo, as if by the pressure of a cuirass.
The sacral bone, (Pl. 5, Fig. 2, a), is united to the pelvis, (p), in a manner peculiar to itself, and calculated to produce extraordinary strength; its processes indicate the existence of very powerful muscles for the movement of the tail. The tail was long, and composed of vertebrae of enormous magnitude, (Pl. 6, Fig. 2), the body of the largest being seven inches in diameter, and

[MEGATHERIUM.] the horizontal distance between the extremities of the two transverse processes, being twenty inches. If to this we add the thickness of the muscles and tendons, and of the shelly integument, the diameter of the tail, at its largest end, must have been at least two feet; and its circumference, supposing it to be nearly circular like the tail of the Armadillo, about six feet. These vast dimensions are not larger in proportion to the adjacent parts of the body, than those of the tail of the Armadillo, and as this animal applies its tail, to aid in supporting the weight of its body and armour, it is probable that the Megatherium made a similar use of the same organ.* To the caudal vertebræ were attached also large inferior spines, or additional Chevron bones, which must have added to the strength of the tail, in assisting to support the body. The tail also probably served for a formidable instrument of defence, as in the Pangolins and Crocodiles. In 1822, Sellow saw portions of armour that had covered a tail, found near Monte Video.

The ribs are more substantial, and much thicker, and shorter, than those of the Elephant

* The tail of the Elephant is remarkably light and slender, with a tuft of coarse hair at its extremity, to brush off flies; that of the Hippopotamus is a few inches only in length, and flattened vertically, to act as a small rudder in swimming.

[162 FOSSIL MAMMALIA.] or Rhinoceros; and the upper convex surfaces of some of them exhibit a rugous and flattened condition of that part, on which the weight of a bony cuirass would most immediately have rested.

The scapula or shoulder blade, (Pl. 6, Fig. 1,f,) resembles that of no other family except the Sloths, and exhibits in the Acromion (g,) contrivances for strength, peculiar to itself and them, in its mode of articulation with the collar bone (Ii); it exhibits also unusual provisions for the support of the most powerful muscles for the movement of the arm.
The clavicle or collar bone (h) is strong, and curved nearly as in the human subject; the presence of this bone in the Megatherium, whilst it is wanting in the Elephant, Rhinoceros, and all the large ruminating animals, shows that the fore-leg discharged some other office, than that of an organ of locomotion . This clavicle would give a steady and fixt position to the socket, or glenoid cavity of the scapula, admitting of rotatory motion in the fore-leg, analogous to that of the human arm. There is in these circumstances a triple accommodation to the form and habits of the Megatherium; 1°. a free rotatory power of the arm was auxiliary to its office, as an

[153 MEGATHERIUM.] instrument to be employed continually in digging food out of the ground; 2°. this act of perpetual digging in search of stationary objects like roots, required but little locomotive power; 3°. the comparatively small support afforded to the weight of the body by the fore-leg, was compensated by the extraordinary and colossal strength of the haunches and hind-legs. In the Elephant, the great weight of the head and tusks require shortness of neck, and unusual enlargement and strength in the fore-legs; hence, the anterior parts of this animal are much stronger and larger than its hinder parts. In the case of the Megatherium, the relative proportions are reversed; the head is comparatively small, the neck is long, and the anterior part of the body but slightly loaded in comparison with its abdominal and posterior regions. In the shoulder blade and collar bone there is great provision to give strength and motion to the fore-legs; but this motion is not progressive, nor is the strength calculated merely to support the weight of the body. The humerus, (k) articulates with the scapula by a round head, admitting of free motion in various directions, and is small at its upper and middle part, but at its lower end attains extraordinary breadth, in consequence of an enormous expansion of the crests, which rise from the condyles, to give origin to muscles for the movement of the fore-foot and

[164 FOSSIL MAMMALIA.] toes.* The ulna (l) is extremely broad and powerful at its upper extremity, affording large space for the origin of muscles, concerned in the movements of the foot. The radius (in) revolves freely on the ulna, as in the Sloths and Anteaters, both of which make much use of the fore-leg, though for different purposes; it has a cavity at its upper end, which turns upon a spherical portion of the lower part of the hu merus, and a large apophysis (n), projecting froni its longitudinal crest, indicates great power in the muscles that gave rotatory motion .

The entire fore-foot must have been about a yard in length, and more than twelve inches wide; forming a most efficient instrument for moving the earth, from that depth within which succulent roots are usually most abundant. This great length of the fore-foot, when resting upon the ground, though unfavourable to progressive motion, must have enabled one fore-leg, when acting in conjunction with the two hind legs and tail, to support the entire weight of the body; leaving the other fore-leg at liberty to be employed exclusively in the operation of digging food.

* There is a similar expansion of the lower part of the Humerus in the Ant-eater, which employs its fore-feet in digging up the solid hills of the Termite Ants.

At Pl. 5, beneath Fig. 1, are represented the fore-foot of an Armadillo (Dasypus Peba), and the fore-foot of the Chlamyphorus, each adapted, like that of the Megatheriam, to form an

[155 MEGATHERIUM] The toes of the fore-foot are terminated by large and powerful claws of great length; the bones, supporting these claws, are composed partly of an axis, or pointed core, (o,) which filled the internal cavity of the horny claw; and partly of a bony sheath, that formed a strong case to receive and support its base. These claws were set obliquely to the ground, like the digging claws of the Mole, a position which made them instruments of greater power, for the purpose of excavation.

The pelvis of the Megatherium (Pl. 6, Fig. 2. p.) is of vast solidity and expanse; and the enormous bones of the ileum (r) are set nearly at right angles to the spine of the back, and at their outer margin, or crest, are more than five feet asunder, very much exceeding the diameter across the haunches of the largest Elephant: the crest of the ileum, (s,) is much flattened, as if by the pressure of the armonr. This enormous size of the pelvis would be disproportionate and inconvenient to an animal of ordinary stature and

instrument of peculiar power for the purpose of digging; and each presenting an extraordinary enlargement and elongation of the extreme bones of the toes, for the support of long and massive claws. At Pl. 5, Figs . 18, 19, the anterior parts of these animals are represented, and show how large a proportion the claws bear to the other parts of the body.

[166 FOSSIL MAMMALIA.] functions; but was probably attended with much advantage to the Megatherium, in relation to its habit of standing great part of its time on three legs, whilst the fourth was occupied in digging.

The pelvis being thus, unusually wide and heavy, presents a further deviation from other animals, as to the place and direction of the acetabulum, or socket which articulates with the head of the thigh bone (u). This cavity, in other animals, is usually set more or less obliquely outwards, and by this obliqmty facilitates the movement of the hind leg; but in the Megatherium it is set perpendicularly downwards, over the head of the femur, and is also nearer than usual to the spine; deriving from this position increase of strength for supporting vertical pressure, but attended with a diminished capability of rapid motion.*

From the enormous width of the pelvis, it

* There is also a further peculiarity for the increase of strength in the manner in which that part, which, in most other animals, is an open space, called the iscitiatic notch (Pl. 5, Fig. 2 c.), is nearly closed with solid bone by the union of the spines of the ischia with the elongated transverse processes of the sacral vertebræ, (a).

Further evidence of the enormous size and powcr in the muscles of the thigh and leg is afforded by the magnitude of the cavity in the sacrum, (Pl. 5. d,) for the passage of the spinal marrow this cavity being about four inches in diameter, the spinal marrow must have been a foot in circumference. The extraordinary magnitude also of the nerves which proceeded from it to supply the leg, is indicated by the prodigious size of the sucral foramina.

[157 MEGATHERIUM.] follows also that the abdominal cavity was ex~ tremely large, and the viscera voluminous, and adapted to the digestion of vegetable food.

The form and proportions of the thigh bone, (v) are not less extraordinary than those of the pelvis, being nearly three times the thickness of the femur of the largest Elephant. Its breadth is nearly half its entire length, and its head is united to the body of the bone by a neck of unusual shortness and strength, twenty-two inches in circumference. Its length is two feet four inches, and its circumference at the smallest part two feet two inches; and at the largest part, three feet two inches. Its body is also flattened; and by means of this flatness, expanded outwards to a degree of which Nature presents no other example. These peculiarities in the femur appear to be subservient to a double purpose: first, to give extraordinary strength by the shortness and solidity of all its proportions; and secondly, to afford compensa tion, by its flatness outwards; for the debility which would otherwise have followed from the inward position of the sockets, (t,) by which the femur, (u,) articulates with the pelvis.

The two bones of the leg (x, y,) are also extremely short, and on a scale of solidity and strength, commensurate with that of the femur that rests upon them. This strength is much increased by their being united at both extremities; an union which is said by Cuvier to

[158 FOSSIL MAMMALIA.] occur in no other animals except the Armadillo and Chlamyphorus; both of which are continually occupied in digging for their food.

The articulation of the leg with the hind-foot is admirably contrived for supporting the enormous pressure of downward weight; the astra galus (z), or great bone of the instep, being nine inches broad, and nine inches high, is in due proportion to the lower extremity of the tibia, or leg bone, with which it articulates; and rests upon a heel bone, of the extraordinary length of seventeen inches, with a circumference of twenty-eight inches. This enormous bone, pressing on the ground, gives a firm bearing and solid support to the continuous accumulation of weigh, which we have been tracing down from the pelvis through the thigh and leg: in fact the heel bone occupies nearly one-half of the entire length of the hind-foot; the bones of the toes are all short, excepting the extreme joint, which forms an enormous claw-bone; larger than the largest of those in the fore-foot, measuring thirteen inches in circumference, and having within its sheath a core, ten inches long, for the support of the horny claw with which it was invested. The chief use of this large claw was probably to keep the hind foot fixed steadily upon the ground.*

*It is probable that the large thick claw, Pl. 5 5', was placed on the second toe of the hind-foot. Its size approaches nearly to that of the first toe of this foot, and both of these differ

[159 MEGATHERIUM.] Feet and legs thus heavily constructed, must have been very inefficient organs of rapid locomotion,  and may consequently seem imperfect, if considered in relation to the ordinary functions of other quadrupeds; but, viewed as instruments adapted for supporting an almost stationary creature, of unusual weight, they claim our admiration equally with every other piece of animal mechanism, when its end and uses are understood. The perfection of any instrument can only be appreciated by looking to the work it is intended to perform. The hammer and anvil of an anchorsmith, though massive, are neither clumsy nor imperfect; but bear the same proportionate relation to the work in which they are employed, as the light and fine tools of the watchmaker bear to the more delicate wheels of his chronometer.

Another remarkable character of the Megatherium, in which it approaches most nearly to the Armadillo, and Chlamyphorus, consists, in its hide having probably been covered with a
bony coat of armour; varying from three-fourths of an inch, to an inch and half in thickness, and

materially in form and proportions, from the three more elongated and flatter claw-bones of the fore-foot, the oblique form of which is peculiarly adapted for digging.

[160 FOSSIL MAMMALIA.] resembling the armour which covers these living inhabitants, of the same warm and sandy regions of South America. Fragments of this armour are represented at Pl. 6, Figs. 12, 13.*

A covering of such enormous weight, would have been consistent with the general structure of the Megatherium ; its columnar hind-legs and colossal tail, were calculated to give it due support; and the strength of the loins and ribs, being very much greater than in the Elephant, seems to have been necessary for carrying so ponderous a cuirass as that which we suppose to have covered the body.

* The resemblance between some parts of this fossil armour, and of the armour of an Armadillo, (Dasypus Peba) is extended even to the detail of the patterns of the tuberculated compartments into which they are divided, see Pl. 5, Figs. 12, 14. The increase of size in the entire shield is in both cases provided for, by causing the centre of every plate to form a centre of growth, around which the margin receives continual additions, as the increasing bulk of the body requires an increase in the dimensions of the bony case, by which it is invested. Figs. 15, 16, 17, represent portions of the armour of the head, body, and tail piece of the Chiamyphorus. Figs . 18, 19, represent the manner in which the armour is disposed over the head and anterior part of the body of the Chlamyphorus, and Dasypus Peba. The body of the Megatherium, when covered with its corresponding coat of armour, must in some degree have resembled a tilted waggon .

In the Transactions of the Academy of Berlin, 1830, Professor Weiss has published an account of some Bones of the Megatherium, discovered near Monte Video, accompanied by several fragments of bony armour. Much of this armour he

[161 MEGATHERIUM.] It remains to consider, of what use this cuirass could have been to the gigantic animal on which it probably was placed. As the locomotive organs of the Megatherium indicate very slow power of progression, the weight of a cuirass would have afforded little impediment to such tardy movements; its use was probably defensive, not only against the tusks and claws of beasts of prey, but also, against the myriads of insects, that usually swarm in such climates as those wherein its bones are found; and to which an animal that obtained its food by digging beneath a broiling sun, would be in a peculiar

refers without doubt to the Megatherium; other portions of it, and also many bones from the same district, he assigns to other animals. A similar admixture of bones and armour, derived from more than one species of animal, bearing a bony cuirass, is found in the collection made at several and distant points of the country above Buenos Ayres, by Mr. Parish. Although no armour was found with the fragmeins of the large skeleton, in the bed of the Salado, the rough broad flattened surface of a part of the crest of the ileum of this skeleton, (see Pl. 5, Fig. 2. r, s,) and the broad condition of the summit of the spinous processes of many vertebræ, and also of the superior convex portion of certain ribs on which the armour would rest, afford evidence of pressure, similar to that we find on the analogous parts of the skeleton of the Armadillo, from which we might have inferred that the Megatherium also was covered with heavy armour, even had no such armour been discovered near bones of this animal in other parts of the same level district of Paraguay. In all these flattened bones the effects of pressure are confined to those parts of the skeleton, on which the armour would rest, and are such as Occur in a remarkable degree in the Armadillo.
 

[162 FOSSIL MAMMALIA.] degree exposed. We may also conjecture it to have had a further use in the protection afforded by it to the back, and upper parts of the body; not only against the sun and rain, but against the accumulations of sand and dust, that might otherwise have produced irritation and disease.*

We have now examined in detail the skeleton of an extinct quadruped of enormous magnitude; every bone of which presents peculiarities, that at first sight appear imperfectly contrived, but which become intelligible when viewed in their

* To animals that dig only occasionally, like Badgers, Foxes, and Rabbits, to form a habitation beneath the ground, but seek their food upon the surface, a defence of this kind would not only have been unnecessary but inconvenient.

The Armadillo and Chlamyphorus are the only known animals that have a compact coat of plated armour, like that of the Megatherium. As this peculiar covering is confined to these quadrupeds, we can hardly imagine its use to be solely for protection against other beasts and insects; but as the Armadillo obtains its food by digging in the same dry and sandy plains, which were once inhabited by the Megatherium, and the Chlamyphorus lives almost entirely in burrows beneath the surface of the same sandy regions; they both probably receive from their cuirass the same protection to the upper parts of their bodies from sand and dust, which we suppose to have been afforded by its cuirass to the Megatherium. The scales of the Chlamyphorus are of a dense substance like hard leather. The Pangolins are covered with a different kind of armour, composed of separate horny moveable scales.

[163 MEGATHERIUM.] relations to one another, and to the functions of the animal in which they occur.

The size of the Megatherium exceeds that of the existing Edentata, to which it is most nearly allied, in a greater degree than any other fossil animal exceeds its nearest living congeners. With the head and shoulders of a Sloth, it combined in its legs and feet, an admixture of the characters of the Ant-eater, the Armadillo, and the Chlamyphorus; it probably also still further resembled the Armadillo and Chlamyphorus, in being cased with a coat of armour. Its haunches were more than five feet wide, and its body twelve feet long and eight feet high; its feet were a yard in length, and terminated by most gigantic claws; its tail was probably clad in armour, and much larger than the tail of any other beast, among extinct or living terrestrial Mammalia. Thus heavily constructed, and ponderously accoutred, it could neither run, nor leap, nor climb, nor burrow under the ground, and in all its movements must have been necessarily slow; but what need of rapid locomotion to an animal, whose occupation of digging roots for food was almost stationary? and what need of speed for flight from foes, to a creature whose giant carcase was encased in an impenetrable cuirass, and who by a single pat of his paw, or lash of his tail, could in an instant have demolished the Couguar or the

[164 FOSSIL MAMMALIA.]  Crocodile? Secure within the panoply of his bony armour, where was the enemy that would dare encounter this Behemoth of the Pampas? or, in what more powerful creature can we find the cause that has effected the extirpation of his race?

His entire frame was an apparatus of colossal mechanism, adapted exactly to the work it hadto do; strong and ponderous, in proportion as this work was heavy, and calculated to be the vehicle of life and enjoyment to a gigantic race of quadrupeds; which, though they have ceased to be counted among the living inhabitants of our planet, have, in their fossil bones, left behind them imperishable monuments of the consummate skill with which they were constructed. Each limb, and fragment of a limb, forming co-ordinate parts of a well adjusted and perfect whole; and through all their deviations from the form and proportion of the limbs of other quadrupeds, affording fresh proofs of the infinitely varied, and inexhaustible contrivances of Creative Wisdom.

[165 FOSSIL SAURIANS.]

IN those distant ages that elapsed during the formation of strata of the secondary series, so large a field was occupied by reptiles, referrible to the order of Saurians, that it becomes an important part of our enquiry to examine the history and organization of these curious relics of ancient creations, which are known to us only in a fossil state. A task like this may appear quite hopeless to persons unaccustomed to the investigation of subjects of such remote antiquity; yet Geology, as now pursued, with the aid of comparative anatomy, supplies abundant evidence of the structure and functions of these extinct families of reptiles; and not only enables us to infer from the restoration of their skeletons, what may have been the external form of their bodies; but instructs us also as to their economy and habits, the nature of their food, and even of their organs of digestion. It further shows their relations to the then existing condition of the world, and to the other forms of organic life with which they were associated.

The remains of these reptiles bear a much greater resemblance to one another, than to those

[166 FOSSIL SAURIANS.] of any animals we discover in deposits preceding or succeeding the secondary series.*

The species of fossil Saurians are so numerous, that we can only select a few of the most remarkable among them, for the purpose of exemplifying the prevailing conditions of animal life, at the periods when the dominant class of animated beings were reptiles; attaining, in many cases, a magnitude unknown among the living orders of that class, and which seems to have been peculiar to those middle ages of geological chronology, that were intermediate between the transition and tertiary formations.

During these ages of reptiles, neither the carnivorous nor lacustrine Mammalia of the tertiary periods had begun to appear; but the most formidable occupants, both of land and water, were Crocodiles, and Lizards; of various forms, and often of gigantic stature, fitted to endure the turbulence, and continual convulsions of the unquiet surface of our infant world.

When we see that so large and important a range has been assigned to reptiles among the

* The oldest strata in which any reptiles have yet been found are those connected with the magnesian-limestone formation. (Pl. 1, Sec. 16). The existence of reptiles allied to the Monitor in the cupriferous slate and zechstein of Germany, has long been known. In 1834, two species of reptiles, allied to the Iguana and Monitor, were discovered in the dolomitic conglomerate, on Durdham Down, near Bristol.

[167 FOSS1L SAURIANS.] former population of our planet, we cannot but regard with feelings of new and unusual interest, the comparatively diminutive existing orders of that most ancient family of quadrupeds, with the very name of which we usually associate a sentiment of disgust. We shall view them with less contempt, when we learn from the records of geological history, that there was a time when reptiles not only constituted the chief tenants, and most powerful possessors of the earth, but extended their dominion also over the waters of the seas; and that the annals of their history may be traced back through thousands of years, antecedent to that latest point in the progressive stages of animal creation, when the first parents of the human race were called into existence.

Persons to whom this subject may now be presented for the first time, will receive, with much surprise, perhaps almost with incredulity, such statements as are here advanced. It must be admitted, that they at first seem much more like the dreams of fiction and romance, than the sober results of calm and deliberate investigation; but to those who will examine the evidence of facts upon which our conclusions rest, there can remain no more reasonable doubt of the former existence of these strange and curious creatures, in the times and places we assign to them; than is felt by the antiquary, who, finding the catacombs of Egypt stored
 

[168 MARINE SAURIANS.] with the mummies of Men, and Apes, and Crocodiles, concludes them to be the remains of mammalia and reptiles, that have formed part of an ancient population on the banks of the Nile.

NEARLY at the head of the surprising discoveries, which have been made relating to the family of Saurians, we may rank the remains of many extraordinary species, which inhabited the sea; and which present almost incredible combinations of form, and structure; adapting them for modes of life, that do not occur among living reptiles. These remains are most abundant throughout the lias and oolite formations of the secondary series.* In these deposits we

* The chief repository in which these animals have been found is the lias, at Lyme Regis; but they abound also along the whole extent of this formation throughout England, e. g. from the coast of Dorset, through Somerset and Leicestershire, to the coast of Yorkshire they are found also in the lias of Germany and France. The range of the genus Ichthyosaurus seems to have begun with the Muschelkalk, and to have extended through the whole of the ooltic period into the cretaceous formation. The most recent stratum in which any remains of this genus have yet been found is the chalk marl at Dover, where they have been discovered by Mr. Mantell: I have found them in the gault near Benson, Oxon.

[169 ICHTHYOSAURUS.] find not only animals allied to Crocodiles, and nearly approaching to the Gavial of the Ganges; but also still more numerous gigantic Lizards, that inhabited the then existing seas and estuaries.

Some of the most remarkable of these reptiles have been arranged under the genus Ichthyosaurus, (or Fish Lizard), in consequence of the partial resemblance of their vertebræ to those of fishes. (See Plate 1, Fig. 51, and Plates 7, 8, 9.) If we examine these creatures with a view to their capabilities of locomotion, and the means of offence and defence, which their extraordinary structure afforded to them; we shall find combinations of form and mechanical contrivances, which are now dispersed through various classes and orders of existing animals, but are no longer united in the same genus. Thus, in the same individual, the snout of a Porpoise is combined with the teeth of a Crocodile, the head of a Lizard with the vertebræ of a Fish, and the sternum of an Ornithorhynchus with the paddles of a Whale. The general outline of an Ichthyosaurus must have most nearly resembled the modern Porpoise, and Grampus. It had four broad feet, or paddles, (Pl. 7), and terminated behind in a long and powerful tail. Some of the largest of these reptiles must have exceeded thirty feet in length .

There are seven or eight known species of the genus Ichthyosaurus, all agreeing with one

[170 MARINE SAURIANS.] another in the general principles of their construction, and the possession of those peculiar organs, in which I shall endeavour to point out the presence of mechanism and contrivance, adapted to their habits and state of life. As it will be foreign to our purpose to enter on details respecting species, 1 shall content myself with referring to the figures of the four most common forms (Plates 7, 8, 9.)*
 
 

The head, which in all animals forms the most important and characteristic part, (see Pl. 10,

* Pl. 7, is a large and nearly perfect specimen of the Ichthyosaurus Platyodon, from the lias at Lyme Regis, being one of the splendid series of Saurians, purchased in 1834 of Mr. Hawkins by the British Museum. Portions of the paddles, and many lost fragments, are restored from the corresponding parts which are preserved; a few vertebræ, and the extremity of the tail are also restored conjecturally. Beautiful and accurate lithographed figures of this specimen, and of the greater part of this collection, are published in Mr. Hawkins's Memoirs of Ichthyosauri and Plesiosauri, London, 1834. Pl. 8. Fig. 1, is a small specimen of the Ichthyosaurus Communis, from the has at Lyme Regis, belonging to the Geol. Soc. of London. Pl. 8, Fig. 2, a small Ichthyosaurus Intermedius, from the has at Lynie Regis belonging to Sir Astley Cooper. Pl. 9, Fig. 1, an Ichthyosaurus Tenuirostris, from the lias of Street, near Glastonbury, in the collection of Rev. D. Williams. Fig. 2 is the continuation of the tail, and Fig. 3, the reverse of the head. The teeth in this species are small, and in due proportion to the slender character of the snout.

[171 ICHTHYOSAURUS.] Figs. 1, 2), at once shows that the Ichthyosauri were Reptiles, partaking partly of the characters of the modern Crocodiles, but more allied to Lizards. They approach nearest to Crocodiles in the form and arrangement of their teeth. The position of the nostril is not, as in Crocodiles, near the point of the snout; it is set, as in Lizards, near the anterior angle of the orbit of the eye. The most extraordinary feature of the head is the enormous magnitude of the eye, very much exceeding that of any living animal.* The expansion of the jaws must have been prodigious; their length in the larger species, (Ichthyosaurus Platyodon), sometimes exceeding six feet; the voracity of the animal was doubtless in proportion to its powers of destruction. The neck was short, as in fishes.
 
 

The teeth of the Iclithyosaurus (Pl. 11, B, C,) are conical, and much like those of the Crocodiles, but considerably more numerous, amounting in some cases to a hundred and eighty; they vary in each species; they are not enclosed in deep and separate sockets, as the teeth of Crocodiles,

* In the collection of Mr. Johnson at Bristol is a skull of Ichthyosaurus Platyodon, in which the longer diameter of the orbital cavity measures fourteen inches.

[172 MARINE SAURIANS.] but are ranged in one long continuous furrow, (Pl. 11, B, C,) of the maxillary bone, in which the rudiments of a separation into distinct alveoli may be traced in slight ridges extending between the teeth, along the sides and bottom of the furrow. The contrivance by which the new tooth replaces the old one, is very nearly the same in the Ichthyosauri as in the Crocodiles (Pl. 11, A, B, C); in both, the young tooth begins its growth at the base of the old tooth, where, by pressure on one side, it causes first a partial absorption of the base, and finally a total removal of the body of the older tooth, which it is destined to replace.*

As the predaceous habits of the Ichthyosauri exposed them, like modern Crocodiles, to frequent loss of their teeth, an abundant provision has in each case been made for their continual renewal .

* In Pl. 11, Fig. A, shows the manner in which the older tooth in the Crocodile becomes absorbed, by pressure of a younger tooth rising within the cavity of its hollow base. Fig. c, represents a transverse section of the left side of the lower jaw of an Ichthyosaurus, showing two teeth in their natural place, within the furrow of the jaw; the younger tooth, by lateral pressures has caused absorption of the inside portion of the base of the older tooth. Fig. B, represents a transverse section of the entire snout of an Ichthyosaurus, in which the lower jaw exhibits on both sides, a small tooth (a), which has caused partial absorption of the base of the larger tooth, (c). In the upper jaw, the bases of two large teeth (d, d,) are seen in their respective furrows.

[173 ICHTHYOSAURUS.]

The enormous magnitude of the eye of the Ichthyosaurus (Pl. 10, Fig. 1, 2), is among the most remarkable peculiarities in the structure of this animal. From the quantity of light admitted in consequence of its prodigious size, it must have possessed very great powers of vision; we have also evidence that it had both microscopic and telescopic properties. We find on the front of the orbital cavity in which this eye was lodged, a circular series of petrified thin bony plates, ranged around a central aperture, where once was placed the pupil; the form and thickness of each of these plates very much resembles that of the scales of an artichoke (Pl . 10, Fig. 3). This compound circle of bony plates, does not occur in fishes; but is found in the eyes of many birds,* as well as of Turtles,

* The bony sclerotic of the Ichthyosaurus approaches to the form of the bony circle in the eye of the Golden Eagle (Pl. 10, Fig. 5); one of its uses in each case being to vary the sphere of distinct vision, in order to descry their prey at long or short distances. These bony plates also assist to maintain the prominent position of the front of the eye, which is so remarkable in birds. In Owls, whose nocturnal habits render distant vision impossible, Mr. Yarrel observes, that the bony circle (Pl. 10, Fig. 4), is concave, and elongated forwards, so that the front of the eye is placed at the end of a long tube, and thus projects beyond the loose and downy feathers of the head; he adds; " The extent of vision enjoyed by the Falcons is probably denied to the Owls, but their more spherical lens and corresponding cornea give them an intensity better suited to the opacity of the medium in which they are required to exercise this

[174 MARINE SAURIANS.] Tortoises, and Lizards; and in a less deg~ee in Crocodiles. (Pl. 10, Figs. 4. 5. 6.)

In living animals these bony plates are fixed in the exterior or sclerotic coat of the eye, and vary its scope of action, by altering the convexity of the cornea: by their retraction they press forward the front of the eye and convert it into a microscope; in resuming their position, when the eye is at rest, they convert it into a telescope. The soft parts of the eyes of the Ichthyosauri have of course entirely perished; but the preservation of this curiously constructed hoop of bony plates, shows that the enormous eye, of which they formed the front, was an optical instrument of varied and prodigious power, enabling the Ichthyosaurus to descry its prey at great or little distances, in the obscurity of night, and in the depths of the sea; it also tends to associate the animal, in which it existed, with the family of Lizards, and exclude it from that of fishes.*

power. They may be compared to a person near-sighted, who sees objects with superior magnitude and brilliancy when within the prescribed limits of his natural powers of vision, from the increased angle these objects subtend." Yarrel on the Anatomy of Birds of Prey, Zool. Journal, v. 3, p. 188.

* There are analogous contrivances for the purpose of resisting pressure, and maintaining the form of the eye in fishes, by the partial or total ossification of the exterior capsule; but in fishes, this ossification is usually simple, though carried to a different extent in different species; and the bone is never divided transversely into many plates, as in Lizards and Birds; these capsules of the eye are often preserved in the heads of fossil fishes: they abound in the London clay; and occasionally occur in chalk.

[175 ICHTHYOSAURUS.] A further advantage resulting from this curious apparatus of bony plates, was to give strength to the surface of so large an eye-ball, enabling it the better to resist the pressure of deep water, to which it must often have been exposed; it would also have protected this important organ from injury by the waves of the sea, to which an eye, sometimes larger than a man's head, must frequently have been subject, when the nose was brought to the surface, for the necessary purpose of breathing air: the position of the nostrils, close to the anterior angle of the eye, rendered it impossible for the Ichthyosaurus to breathe without raising its eye to the surface of the water.
 
 

The Jaws of the Ichthyosauri, like those of Crocodiles and Lizards, which are all more or less elongated into projecting beaks, are composed of many thin plates, so arranged as to combine strength with elasticity and lightness, in a greater degree than could have been effected by single bones, like those in the jaws of Mammalia. It is obvious that an under jaw so slender, and so much elongated as that of a Crocodile or Ichthyosaurus, and employed in seizing and retaining the large and powerful animals which formed their prey, would have been comparatively weak and liable to fracture

[176 MARINE SAURIANS.] if composed of a single bone. Each side of the lower jaw was therefore made up of six separate pieces, set together in a manner that will be best understood by reference to the Figures in Pl. 11.*

This contrivance in the lower Jaw, to combine the greatest elasticity and strength with the smallest weight of materials, is similar to that adopted in binding together several parallel plates of elastic wood, or steel, to make a cross-bow; and also in setting together thin plates of steel in the springs of carriages. As in the carriage spring, or compound bow, so also in the compound jaw of the Ichthyosaurus, the plates are most numerous and strong, at the parts where the greatest strength is required to be exerted; and are thinner, and fewer, towards the extremities, where the service to be performed is less severe. Those who have

* These figures are selected from various plates by Mr. Cony beare and Mr. De la Beche. Fig. 1 is a restoration of the entire head of an Ichthyosaurus, in which each component bone is designated by the letters appropriated by Cuvier to the equivalent bones in the head of the Crocodile. In the lower jaw, u, marks the dental bone; v, the angular bone; x, superangrular or coronoid; y, articular bone; z, complementary; &, opercular. Fig. 2, is part of an under jaw of an Ichthyosaurus, showing the manner in which the flat bones, v, x, u, are applied to each other, towards the posterior part of the jaw. Figs. 3, 4, 5, 6, 7, show the manner in which these bones overlap, and lock into each other, at the transverse sections, indicated by the lines immediately above them in Fig. 2. Fig. 8, shows the composition of the bones in the lower jaw, as seen from beneath.

[177 ICHTHYOSAURUS.] witnessed the shock given to the head of a Crocodile, by the act of snapping together its thin long jaws, must have seen how liable to fracture the lower jaw would be, were it composed of one bone only on each side: a similar inconvenience would have attended the same simplicity of structure in the jaw of the Ichthyosaurus. In each case, therefore, the splicing and bracing together of six thin flat bones of unequal length, and of varying thickness, on both sides of the lower jaw, affords compensation for the weakness and risk of fracture, that would otherwise have attended the elongation of the snout.

Mr. Conybeare points out a further beautiful contrivance in the lower jaw of the Ichthyosaurus, analogous to the cross bracings lately introduced in naval architecture, (see Pl. 11, Fig. 2.)*

The vertebral column in the Ichthyosaurus was composed of more than one hundred joints; and

* The coronoid bone, (x) is interposed between the dental, (u), and opercular (&), its fibres having a slanting direction, whilst those of the two latter bones are disposed horizontally; thus, the strength of the part is greatly increased by a regular diagonal bracing, without the least addition of weight or bulk; a similar structure may be noticed in the overlapping bones of the heads of fish, and in a less degree, in those of Turtles — Geol. Trans. Lond. Vol. V. p. 565, and Vol. l. N. S. p 112.

[178 MARINE SAURIANS.] although united to a head nearly resembling that of a Lizard, assumed, in the leading principles of its construction, the character of the vertebrae of fishes. As this animal was con structed for rapid motion through the sea, the mechanism of hollow vertebrae, which gives facility of movement in water to fishes, was better calculated for its functions than the solid vertebræ of Lizards and Crocodiles.* (See Plate 12, A. and B.) This hollow conical form would be inapplicable to the vertebræ of land quadrupeds, whose back, being nearly at right angles to the legs, requires a succession of broad and nearly flat surfaces, which press with considerable weight against

* The sections of the vertebrae of a fish (A c. c.) present two hollow cones, united at their apex in the centre of each vertebra, in the form of an hour-glass; but the base of each cone, (b. b.) instead of terminating in a broad flat surface, like the base of the hour-glass, is bounded by a thin edge, like the edge of a wine glass, and by this alone touches the corresponding edge of the adjacent vertebra. Between these hollow vertebræ, a soft and flexible intervertebral substance, in the form of a double solid cone (e. e.) is so placed that each hollow cone of bone plays on the cone of elastic substance contained within it, with a motion in every direction; thus forming a kind of universal joint, and giving to the entire column great strength, and power of rapid flexion in the water. But as the inflections in the perpendicular direction are less necessary than in the lateral, they are limited by the overlapping, or contiguity of the spines.

This mode of articulation gives mechanical advantage to animals like fishes, whose chief organ of progressive motion is the tail; and the weight of whose bodies being always suspended in water, creates little or no pressure on the edges, by which alone the vertebræ touch each other.

[179 ICHTHYOSAURUS.] each other. It is quite certain, therefore, that such large and bulky creatures as the Ichthyosauri, having their vertebra constructed after the manner of fishes, had they been furnished with legs instead of paddles, could not have moved on land without injury to their backs.*

The ribs were slender, and most of them bifurcated at the top: they were also continuous along the whole vertebral column, from the head to the pelvis, (see Plates 7, 8, 9); and in this respect agree with the structure of modern Lizards. A considerable number of them were united in front across the chest: their mode of articulation may be seen in Pl. 14.

Sir E. Home has further remarked a peculiarity of the spinal canal, which exists in no other animals; the annular part (Pl. 12, D a. and E a.) being neither consolidated with the body of the vertebra, as in quadrupeds; nor connected by a suture, as in Crocodiles; but remaining always distinct, and articulating by a peculiar joint, resembling a compressed oval ball and socket joint, (D g. and E g.). And Mr. Conybeare adds, that this mode of articulation co-operates with the cup-shaped form of the interver tebral joints, in giving flexibility to the vertebral column, and assisting its vibratory motions; for, had these parts been consolidated, as in quadrupeds, their articulating processes must have locked the whole column together, so as to render such a motion of its parts impossible; but by means of this joint every part yields to that motion. The tubercle by which the transverse apophysis of the head of the rib articulates with the vertebra, is seen at d.

[180 MARINE SAURIANS.] The ribs of the right side were united to those of the left, by intermediate bones, analogous to the cartilaginous intermediate and sternal portions of the ribs in Crocodiles; and to the bones which, in the Plesiosaurus, form what Mr. Co~nybeare has called the sterno-costal arcs. (See Pl. 17.) This structure was probably subservient to the purpose of introducing to their bodies an unusual quantity of air; the animal by this means being enabled to remain long beneath the water, without rising to t.he surface for the purpose of breathing.*

* The sterno-costal ribs probably formed part of a condensing apparatus, which gave these animals the power of compressing the air within its lungs, before they descended beneath the water. In the Lond. and Edin. Phil. Mag. Oct. 1833, Mr. Faraday has noticed a method of preparing the organs of respiration in man, so as considerably to extend the time of holding the breath in an impure atmosphere; or under water, as practised by pearl-fishers; and illustrated by experiments of Sir Graves C. Houghton. If a person inspires deeply, and ceasing with his lungs full of air, holds his breath as long as he is able, the time during which he can remain without breathing will be double, or more than double, that which he could do if he held his breath without such deep inspiration. When Mr. Brunel, jun. and Mr. Gravatt descended in a diving-bell to examine the hole where the Thames had broken into the tunnel at Rotherhithe, at the depth of about thirty feet of water, Mr. Brunel, having inspired deeply the compressed air within the diving-bell, descended into the water below the bell; and found that he could remain twice as long under water, going into it from the diving-bell at that depth, as he could under ordinary circumstances.

Mr. Gravatt has also informed me that he is able to dive, and remain three minutes under water, after inflating his lungs with

[181  ICHTHYOSAURUS.]

To a marine animal that breathed air, it was essential to possess an apparatus whereby its ascent and descent in the water may have been easily accomplished; accordingly we find such an apparatus, constructed with prodigious strength, in the anterior paddles of the Ichthyosaurus; and in the no less extraordinary coinbination of bones that formed the sternal arch, or that part of the chest, on which these paddles rested. Pl. 12, Fig. l.

It is a curious fact, that the bones composing the sternal arch are combined nearly in the same manner as in the Ornithorhynchus * of New Holland; which seeks its food at the bottom of lakes and rivers, and is obliged, like the

the largest possible quantity of common air, by a succession of strong and rapid inspirations, and immediately compressing the lungs thus filled with air, by muscular exertion, and contraction of the chest, before he plunges into the water. By this compression of the lungs, the specific gravity of the body is also increased, and the descent is consequently much facilitated.

All these advantages were probably united in the mode of respiration of the Ichthyosaurus, and also in the Plesiosaurus.

* In this anomalous animal the Ornithorhynchus or Platypus, we have a quadruped clothed with fur, having a bill like a duck, with four webbed feet, suckling its young, and most probably ovo-viviparous: the male is furnished with spurs. — See Mr. R. Owen's Papers on the Ornithorhynchus Paradoxus, in the Phil. Trans. London, 1832, Part II. and 1834, Part II. See also Mr. Owen's Paper on the same subject in Trans. Zool. Soc. London. Part III. 1835, in which he points out many approximations in the generative and other systems of this animal to the organization of reptiles.

[182 MARINE SAURIANS.] Ichthyosaurus, to be continually rising to the surface to breathe air.*

Here then we have a race of animals that became extinct at the termination of the secondary series of geological formations, presenting, in their structure, a series of contrivances, the same in principle, with those employed at the present day to effect a similar purpose in one of the most curiously constructed aquatic quadrupeds of New Holland.

Paddles.

In the form of its extremities, the Ichthyosaurus deviates from the Lizards, and approaches the Whales. A large animal, moving rapidly through the sea, and breathing air, must have

* In both these animals there is superadded to the ordinary type of bones in quadrupeds, an enlargement of the coracoid bone (c), and a peculiar form of sternum, resembling the furcula of birds. In Pl. 12, Fig. 1, a. represents the peculiar sternum or furcula; b. b. the clavicles; c. c. the coracoid bones; d. d. the scapulæ; e. e. the humeri; f. g. the radius and ulna. At Fig. 2, the same letters are attached to the corresponding bones of the Ornithorhynchus.

The united power of all these bones imparts to the chest and paddles peculiar strength for an unusual purpose; not so much to effect progressive motion (which, in the Ichthyosaurus, was produced with much greater facility and power by the tail), as to ascend and descend vertically in quest of air and food.

The Echidna, or spiny Ant-eater, of New Holland, is the only known land quadruped that has a similar furcula and clavicles. As this animal feeds on Ants, and takes refuge in deep burrows, this structure may be subsidiary to its great power of digging. A cartilaginous rudiment of a furcula occurs also in the Dasypus; and seems subservient to the same purpose.

[183 ICHTHYOSAURUS.] required great modification of the fore-leg and foot of the Lizard, to fit it for such cetaceous habits. The extremities were to be converted into fins instead of feet, and as such we shall find them to combine even a still greater union of elasticity with strength, than is presented by the fin or paddle of the Whale. Plate 12, Fig. 1, shows the short and strong bones of the arm (e), and those of the fore arm (f, g); and be yond these the series of polygonal bones that made up the phalanges of the fingers. These polygonal bones vary in number in different species, in some exceeding one hundred; they differ also in form from the phalanges both of Lizards and Whales; and derive, from their increase of number, and change of dimensions, an increase of elasticity and power. The arm and hand thus converted into an elastic oar or paddle, when covered with skin, must have much resembled externally the undivided paddle of a Porpoise or Whale. The position also of the paddles on the anterior part of the body was nearly the same; to these were super-added posterior extremities, or hind fins, which are wanting in the cetacea, and which possibly make compensation for the absence of their flat horizontal tail: these hind paddles in the Ich thyosaurus are nearly by one half smaller than the anterior paddles.*

* in the Ornithorhynchus, also, the membranous expansion, or web of the hind feet, is very much less than that on the fore foot.

[184 MARINE SAURIANS.] Mr. Conybeare remarks, with his usual acumen, that " the reasons of this variation from the proportions of the posterior extremities of quadrupeds in general, are the same which lead to a similar diminution of the analogous parts in Seals, and their total disappearance in the cetacea, namely, the necessity of placing the centre of the organs of motion, when acting laterally, before the centre of gravity. For the same reason, the wings of birds are placed in the fore part of their body, and the centre of the moving forces given to ships by their sails, and to steam boats by their paddles, is similarly placed. The great organ of motion in fishes, the tail, is indeed posteriorly placed, but this by its mode of action generates a vis a tergo, which impels the animal straight forwards, and does not therefore operate under the same conditions with organs laterally applied." G. T. V. 5, p. 579.

I shall conclude this detailed review of the peculiarities of one of the most curious, as well as the most ancient, among the many genera of extinct reptiles presented to us by Geology, with a few remarks on the final causes of those deviations from the norinal structure of its proper type, the Lizard; under which the Ichthyosaurus combines in itself the additional characters of the fish, the Whale, and Ornithorhynchus. As the form of vertebræ by which it is associated with the class of fishes, seems to have been

[185 ICHTHYOSAURUS.] introduced for the purpose of giving rapid mo tion in the water to a Lizard inhabiting the element of fishes; so the further adoption of a structure in the legs, resembling the paddles of a Whale, was superadded in order to convert these extremities into powerful fins. The still further addition of a furcula and clavicles, like those of the Ornithorhynchus, offers a third and not less striking example of selection of contrivances, to enable animals of one class to live in the element of another class.

If the laws of co-existence are less rigidly maintained in the Ichthyosaurus, than in other extinct creatures which we discover amid the wreck of former creations, still these deviations are so far from being fortuitous, or evidencing imperfection; that they present examples of perfect appointment and judicious choice, pervading and regulating even the most apparently anomalous aberrations.

Having the vertebræ of a fish, as instruments of rapid progression; and the paddles of a Whale, and sternum of an Ornithorhynchus, as instruments of elevation and depression; the reptile Ichthyosaurus united in itself a combination of mechanical contrivances, which are now distributed among three distinct classes of the animal kingdom. If, for the purpose of producing vertical movements in the water, the sternum of the living Ornithorhynchus assumes

[186 MARINE SAURIANS.] forms and combinations that occur but in one other genus of Mammalia, they are the same that co-existed in the sternum of the Ichthyosaurus of the ancient world; and thus, at points of time, separated from each other by the intervention of incalculable ages, we find an identity of objects effected by instruments so similar, as to leave no doubt of the unity of the design in which they all originated.

It was a necessary and peculiar function in the economy of the fish-like Lizard of the ancient seas, to ascend continually to the surface of the water in order to breathe air, and to descend again in search of food; it is a no less peculiar function in the Duck-billed Ornithorhynchus of our own days, to perform a series of similar movements in the lakes and rivers of New Holland.

The introduction to these animals, of such aberrations from the type of their respective orders, to accommodate deviations from the usual habits of these orders, exhibits an union of compensative contrivances, so similar in their relations, so identical in their objects, and so perfect in the adaptation of each subordinate part, to the harmony and perfection of the whole; that we cannot but recognize throughout them all, the workings of one and the same eternal principle of Wisdom and Intelligence, presiding from first to last over the total fabric of Creation.