. Elements of Comparative Anatomy. 488 COMPARATIVE ANATOMY. are attached to tlie leg; these are the fibulare, intermedium^ and tibiale. There are two centralia ; and five distal tarsalia carry the bones of the metatarsus (cf. Fig. 265). In the Enaliosaurii the skeletal portions of the hinder extremity- are an exact repetition of those of the anterior one; and even in some of the Amphibia (Urodela) we meet with an arrangement which is the same in all essential points^ so that we need not describe them specially. In most Urodela, all the five terminal pieces, or toes, are retained in the hind-li
. Elements of Comparative Anatomy. 488 COMPARATIVE ANATOMY. are attached to tlie leg; these are the fibulare, intermedium^ and tibiale. There are two centralia ; and five distal tarsalia carry the bones of the metatarsus (cf. Fig. 265). In the Enaliosaurii the skeletal portions of the hinder extremity- are an exact repetition of those of the anterior one; and even in some of the Amphibia (Urodela) we meet with an arrangement which is the same in all essential points^ so that we need not describe them specially. In most Urodela, all the five terminal pieces, or toes, are retained in the hind-limb; this is more distinctly like the primitive form than is the skeleton of the fore-limb. In Cryptobranchus, Menopoma, and others, the two centralia even are per- sistent. But in the Anura there is a very great change; the tibia and fibula are fused. In the place of the three proximal tarsal bones there are two long bones, which are, however, often fused at their ends; they are ordinarily known as the astragalus and calcaneum. The distal row of tarsal bones is also greatly reduced. Finally, we must note the presence of a rudiment of a sixth toe. § 368. In the Chelonii there are unimportant modifications in the larger pieces of the extremities; in addition to this we must note the gradual concrescence of some of the bones of the tarsus, which is of gi'eat importance as explaining the ske- leton of the foot in Birds, as well as in other Reptiles. An intermedium is united with a tibiale to form an astragalus; and the centrale is attached to, or even com- pletely fused with, this bone. The fourth and fifth tarsalia similarly form a single bone, the cuboid. Owing to the forma- tion of a single piece out of the bones of the first tarsal row, and the firm union that is effected between this piece, and the tibia and fibula, the foot gets to be articulated in a peculiar manner. It moves on an intertarsal joint. The skeleton of the Crocodile's foot is somewhat different. The tibia and
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