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at the bottom of lakes and rivers* and is obliged, like the 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.!
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 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 beyond 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 superadded 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 Ichthyosaurus are nearly by one half smaller than the anterior paddles.*
a quadruped clothed with fur, having a bill like a duck, with four webbed feet, suckling its young, and most properly ovoviviparous I the male is furnished with spurs.—See Mr. [R. Owen's Papers on the Ornithorhynchus Paradoxus, ia 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. Lond. Part III. 1835, in which he points out many approximations in the generative and other systems of this animal to the organisation of reptiles.
* 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 PI. 12, Fig. 1, a. represents the peculiar sternum or furcula; b. b. the clavicles; c. c. the coracoid bones: d. d. the scapulae; 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.
t 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.
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.
* In the Omithorhync'ius, also, the membraneous expansion, or web of the hind feet, is very much less than that on the fore-foot.
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 normal 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 vertebrae by which it is associated with the class of fishes, seems to have been introduced for the purpose of giving rapid motion in the water to a Lizard inhabiting the element of fishes; so the farther 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 farther 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 vertebrae 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 th: water, the sternum of the living Ornilhorhynchus assumes 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 a 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 recognise 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.
INTESTINAL STRUCTURE OF ICHTHYOSAURUS AND OP FOSSIL FISHES.
From the teeth and organs of locomotion, we come next to consider those of digestion in the Ichthyosaurus. If there be any point in the structure of extinct fossil animals, as to which it should have seemed hopeless to discover any kind of evidence, it is the form and arrangement of the intestinal organs; since these soft parts, though of prime importance in the animal economy, yet being suspended freely within the cavity of the body, and unconnected with the skeleton, would leave no traces whatever upon the fossil bones.
It is impossible to have seen the large apparatus of teeth, and strength of jaws, which we have been examining in the Ichthyosauri, without concluding that animals furnished with such powerful instruments of destruction, must have used them freely in restraining the excessive population of the ancient seas. This inference has been fully confirmed by the recent discovery within their skeletons, of the halfdigested remains of fishes and reptiles, which they had devoured, (see PI. 13, 14,) and by the farther discovery of Coprolites, (see PI. 15,) i. e. of foecal remains in a state of petrifaction, dispersed through the same strata in which these skeletons are buried. The state of preservation of these very curious petrified bodies is often so perfect, as to indicate not only the food of the animals from which they were derived, but also the dimensions, form, and structure of their stomach, and intestinal canal.*
* The following description of these Coprolites, is given in my memoir on this subject, published in the Transactions of the Geologioal