xi MUSCLES 505 



middle row is a single Done, the centrale (nai'icular) of the 

 tarsus, and the distal row is made up of three bones, 

 the true first, together with the corresponding digit 

 (hallux}, being absent as a distinct bone. The second 

 (apparent first) distal tarsal articulates proximally \\ith 

 the centrale, and distally with the innermost (preaxial) 

 metatarsal : the third (apparent second) with the 

 centrale and the corresponding metatarsal : 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 correspond- 

 ing 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 com- 

 plicated. 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, 



PRACT. Zoou I I 



