The five digits of the foot each consist of a metatarsal and of a certain number of phalanges. In the specimen examined, owing to the shifting of tarsale 1, the first metatarsal as well as the second articulates with tarsale 2, while the fifth metatarsal articulates partially with the bone representing the fused tarsalia 4 and 5, partially with the fibulare. All the bones of the digits except the distal phalanges are terminated at each end by cartilaginous epiphyses, the distal phalanx of each digit has a cartilaginous epiphysis only on its proximal end.
The first, second, and fifth digits have two phalanges apiece, the third and fourth have three.
Figure 31 B, showing a Newt's tarsus copied from Gegenbaur, has precisely the arrangement generally regarded as primitive for the higher vertebrates, except that tarsalia 4 and 5 are fused.
CHAPTER XI.
THE SKELETON OF THE FROG[55] (Rana temporaria).
I. EXOSKELETON.
The skin of the frog is smooth and quite devoid of scales or other exoskeletal structures. The only exoskeletal structures met with in the frog are:—
1. The teeth, which are most conveniently described with the endoskeleton.
2. The horny covering of the calcar or prehallux (see p. 167).