Comparing them extremities with those of other vertebrated animals we trace a regular series of links and gradations, from the corresponding parts of the highest mammalia, to their least perfect form in the fins of fishes. In the fore paddle of the Plesiosaurus, we have all the essential parts of the fore leg of a quadruped, and even of a human arm; first the scapula, next the humerus, then the radius and ulna, succeeded by the bones of the carpus and metacarpus, and these followed by five fingers, each composed of a continuous series of phalanges. (See Pl. 16, 17, 19.) The hind paddle also offers precisely the same analogies to the leg and foot of the Mammalia; the pelvis and femur are succeeded by a tibia and fibula, which articulate with the bones of the tarsus and metatarsus, followed by the numerous phalanges of five long toes.
From the consideration of all its characters, Mr. Conybeare
has drawn the following inferences with respect to
the habits of the Plesiosaurus Dolichodeirus, "That it was
aquatic is evident, from the form of its paddles; that it was
marine is almost equally so, from the remains with which
it is universally associated; that it may have occasionally
visited the shore, the resemblance of its extremities to those
of the Turtle may lead us to conjecture; its motion however
must have been very awkward on land; its long neck
must have impeded its progress through the water; presenting
a striking contrast to the organization which so admirably
fits the Ichthyosaurus to cut through the waves.
ber to accommodate them to the corresponding office of a paddle. The mode of connexion between the joints was (like that in the Whales,) by synchondrosis. The phalanges of the Plesiosaurus present a link, between the still more numerous and angular joints of the paddle of the Ichthyosaurus, and the phalanges of land quadrupeds, which are more or less cylindrical; in these sea Lizards they were flattened, for the purpose of giving breadth to the extremities as organs of swimming. As its paddles give no indication of having carried even such imperfect claws, as those of the Turtle and Seals, the Plesiosaurus apparently could have made little or no progress in any other element than water.
