xi MUSCLES 505 



with the corresponding digit (hallux\ being absent as a 

 distinct bone. The second (apparent first) distal tarsal 

 articulates proximally with the centrale, and distally with 

 the innermost (preaxial) metatarsal : the third (apparent 

 second) with the astragalus and the corresponding meta- 

 tarsal : the fourth (apparent third), which corresponds to 

 the two fused outer (postaxial) tarsals, with the centrale, 

 calcaneum, and the remaining two digits. 



The foot or pes consists of four metatarsals with their 

 phalanges, of which there are three to each digit. The 

 metatarsal of the hallux, together with the corresponding 

 distal tarsal, is probably represented by a distinct ossification 

 which in the adult becomes fused with the second (apparent 

 first) metatarsal, and forms a process on that bone which 

 articulates with the centrale. The phalanges are similar to 

 those of the manus, and sesamoid bones are also present on 

 the under surface of the foot. 



Muscles and Body-wall. It will be remembered that in 

 the lancelet and dogfish the muscles of the trunk are 

 divided up into myomeres (pp. 419 and 434), while in the 

 adult frog the only indication of such a segmentation of the 

 muscles is seen in the recti of the abdomen. In the rabbit 

 nearly all trace of a segmentation of the muscles has also 

 disappeared, and the muscular system, although similar in its 

 general arrangement to that of the frog (compare Fig. 16) 

 is more highly differentiated and complicated. We shall 

 have occasion to notice certain of the muscles in the course 

 of our examination of other organs. 



Immediately beneath the skin, which consists of epiderm 

 and derm (Fig. 131), the whole ventral region of the trunk 

 and neck is covered by a thin cutaneous muscle, by means of 

 which the rabbit is able to twitch its skin. Internally to 



