xir PHYLUM CHORDATA 407 



thigh is directed downwards, outwards and forwards from 

 the thigh-joint, the shank inwards, backwards and upwards 

 from the knee. The foot consists of two parts, a tarsal 

 region directed downwards from the heel-joint, and five 

 long, slender digits united by thin folds of skin or webs. 

 Thus the limbs are placed in such a way that the elbow and 

 knee face one another, and the first digit that of the hand 

 probably representing the second or index-finger^ that of the 

 foot, the hallux or great toe is turned inwards or towards 

 the median plane of the body. 



The skin is soft and slimy owing to the secretion of 

 mucous glands ; there is no trace of an exo-skeleton. 



The vertebral column (Fig. 231) is remarkable for its 

 extreme shortness ; it consists of only nine vertebrae (v. i 

 v. 9), the last followed by a slender, bony rod, the urostyle 

 (UST). The second to the seventh vertebrae are similar 

 in character. The centrum (B, en.) is somewhat depressed, 

 and has a concave anterior, and a convex posterior face a 

 form known as proccelons. Each half of the neural arch 

 consists of two parts, a pillar-like pedicle (pd.) springing 

 from the centrum and extending vertically upwards, and 

 a flat, nearly horizontal lamina (fm.\ forming, with its fellow, 

 the roof of the neural canal. 



The zygapophyses (a. zyg.) or yoking processes are far 

 better developed than in any fish. Laterally the neural arch 

 gives off on each side a large outstanding transverse 

 Process (tr.pr.) its crown is produced into a very small and 

 inconspicuous neural spine. The first or cervical vertebra 

 (v. i) has a very small centrum and no transverse processes. 

 There are no anterior zygapophyses, but at the junction of 

 centrum and arch, there occurs on each side a large oval 

 concave facet for articulation with one of the condyles of the 

 skull 'see p. 408). The eighth vertebra has a biconcave 



