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The shoulder-bone, already alluded to, works upon
a kind of blade-bone, but is not fitted into a deep socket. Its form somewhat resembles that of the corresponding bone in birds; and this bone, as well as the two which represent the fore-arm, are distinct, but very short and broad in proportion to their length, especially the two latter, which. are often nearly round, and sometimes broader than they are long. Then come a number of small round bones, which represent those of the wrist, and complete two ill-defined rows. After them succeed a multitude of little bones (see figure), arranged in distinct rows and fitting one another, but not exhibiting any mark of that division into fingers, which may be traced in the
skeleton even of the most aquatic of the mammalia. The bones increase in number as they diminish in size, to the termination of the paddle. They form from three to six series, and are so dovetailed together as to constitute an uniformly resisting framework, acting as a simple oar.
Such was the skeleton of this fin, or paddle, as made known by various examples, some of them quite perfect; but we are fortunately in a condition to
tell yet more of its structure, and thence deduce more clearly the habits of the animal.
In one specimen of the paddle (fig. 62), obtained from Barrowupon-Soar, in Leicestershire, not only the bones, but the actual outlines of the extremity of the fin, are clearly defined, and are found to exhibit the impression of a number of rays extending downwards and forking off towards the end. It is clear, from the extreme rarity of their preservation, that these rays were not bony, and they were probably either cartilaginous, or formed of that albuminous horn-like tissue, of which the marginal rays of the shark's fin consist. The fore part of the fin was terminated by a small unbroken and well-defined line, probably only a thickening of the skin; and the dimensions of the soft part, compared with the skeleton, show that the total length of the extremity would be about half as much again as that of its bony and solid portion.
The tail of the Ichthyosaurus was of great length, the number of vertebræ extending beyond the hinder extremities being very much greater than half the whole number possessed by the animal. At about the 30th vertebra from the pelvis there have been observed, in most of the more perfect specimens, distinct marks of a fracture, this portion of the tail being generally bent off at an angle. At the same point, too, there is generally a slight displacement of a few of the bones. This, however, is not all. At the point thus indicated a modification of the form of the vertebra has been observed, so that the rest (forming the tail) have a somewhat oblong shape, just the reverse of what is known to occur in the whale, where these bones are a little flattened. Now
in the whales there is a powerful horizontal tail, by the beating of which up and down against the water, the animal is enabled at once to sink or raise itself in the water with extreme rapidity and force; but the only indication of such a tail in the skeleton consists of this slight flattening in a horizontal direction. From the position and regularity of appearance of the fractured tail of the Ichthyosaurus, and from the shape of the vertebræ, it has been concluded that this animal was provided with a long vertical tail, like that of fishes*; and, as we know that it was amply provided with paddles which would enable it to rise or sink very readily, such a tail would be of the greatest possible utility in producing rapid motion through the water-a power possessed to an almost incredible extent by some of the larger and more voracious fishes, such as the shark, and one which in them transcends any locomotive power that man has yet been able to attain, exceeding even that which birds possess in their familiar element the air. It should not be forgotten that a powerful vertical tail would be almost necessary to the Ichthyosaurus to enable it to turn with precision and rapidity, so that its elongated head should be able to make a sudden and sure seizure of the anticipated prey.
Having now mentioned successively the most striking peculiarities of each part of the skeleton of this animal, and having even drawn conclusions with
After the death of the animal the vertebral column would very soon tend to fall asunder, owing to the absence of connecting processes, and the deep interspaces filled with fluid that existed between each pair of vertebræ. The mere weight of a vertical tail falling on one side would thus drag with it a portion of the bony series, and produce the dislocation so often observed.
regard to such parts as the cartilaginous fins of the paddle, and the position and shape of the tail, or rather tail-fin, the reader will naturally conclude that the subject is exhausted, and that it remains only to sum up into a general view these various details. But the case is not so. We have seen that in this bed of fine mud, the bodies of animals were deposited and preserved so completely, that the skeletons, after the soft parts had decayed, retained their relative position, exhibiting all the important points of structure. Circumstances, however, sometimes occurred by which individuals, overtaken perhaps by sudden destruction, have been at once embedded, a perfect cast being formed of every part, internal as well as external, so that the skin, the contents of the stomach, its proportional magnitude and other details, may be learnt by careful study of the specimens thus embalmed and handed down to us. But, before dwelling upon these obscure and minute points, there are others to be mentioned scarcely less curious, resulting from the continued resort of great families of these monsters to particular spots. Possibly these spots may have been good feeding-ground, and favourable for the development of the larger mollusca and fishes, or the presence of shallows and neighbouring land may have been especially advantageous for breeding; but, at any rate, it is certain that we find, here and there, localities where vast multitudes of pellets of an oval shape and various size are accumulated. These pellets often contain fragments of bone, teeth, or fish scales, and are now recognized as being beyond question the fossilized dung of the great marine reptiles. They are spoken of by Geologists under the name of Co
prolites,* or dung-stones (fig. 63). From the examination of these fossils it is easy to determine the nature of the food of the animals and some other points; and when, as happened occasionally, the animal was killed while the process of digestion was going on, the stomach and intestines being partly filled with half digested food, and exhibiting the coprolites actually in situ, we can make out with certainty, not only the true nature of the food, but the proportionate size of the stomach, and the length and nature of the intestinal canal.
Within the cavity of the ribs of an extinct animal, the palæontologist thus finds recorded in indelible characters some of those hieroglyphics upon which he founds his history. He learns, that of this animal, manifestly well adapted for the most predaceous habits, the stomach formed a pouch of prodigious size, extending through nearly the entire cavity of the body. It was therefore of a capacity well proportioned to the powerful jaws and teeth which were admirably and beautifully contrived to supply its wants. With this enormous stomach, there was, however, very little room for a corresponding intestinal canal, and it is interesting to find the shape of the coprolites distinctly showing that this part of the animal economy in the Ichthyosaurus, as in the most voracious of the existing fishes,
* Kожроç (copros), dung; Xiloç (lithos), a stone. There are strata, many square miles in extent, almost made up of these fossils.