CLASS AMPHIBIA 495 



(Fig. 418, D, Ha) curve upward and join the prootics on either 

 side. Two ossified posterior processes, the thyrohyals (Hp) 

 help support the larynx. 



The Vertebral Column (Fig. 418). — The vertebral column 

 consists of nine vertebra and a blade-like posterior extension, 

 the urostyle. The vertebrae consist of a basal centrum, which 

 is concave in front and convex behind (proccelous type), and a 

 neural arch (Fig. 418, ar) through which the spinal cord passes. 

 The neural arch possesses a short, dorsal spine, a transverse 

 process (trv) on each side (except on the first vertebra, av), and 

 a pair of articulating processes, called zygapophyses (zyg), at 

 each end. The vertebras are held together by ligaments, and 

 move on one another by means of the centra and zygapophyses. 

 The vertebral column thus serves as a firm axial support which 

 also allows bending of the body. 



The Appendicular Skeleton. — The pectoral girdle and 

 sternum (Fig. 419, A) support the fore limbs, serve as attach- 

 ments for the muscles that move the fore limbs, and protect the 

 organs lying within the anterior portion of the trunk. They 

 are composed partly of bone and partly of cartilage. The supra- 

 scapular lie above the vertebral column, and the rest of the girdle 

 passes downwards on either side and unites with the sternum 

 in the ventral, middle line. The principal parts are the supra- 

 scapulcB (Fig. 419, A, s. sc), the scapula (sc), the clavicles (d), 

 the coracoids (cor), the epicoracoids (ep.c), the ommo sternum (os), 

 episternum (ep), mesosternum (mes), and xiphisternum (xi). 

 The end of the long bone of the fore limb (humerus) lies in 

 a concavity in the scapula and coracoid called the glenoid 

 fossa (gl). 



The pelvic girdle (Fig. 419, B) supports the hind limbs. 

 It consists of two sets of three parts each, the ilium (IT), the 

 ischium (Isch), and the pubis (Pu). The pubis is cartilaginous. 

 The anterior end of each ilium is attached to one of the trans- 

 verse processes of the ninth vertebra. Where the parts of each 

 half of the pector al girdle unite, there is a concavity, called 



