238 



THE BIOLOGY OF THE FROG 



The first vertebra, or atlas, differs from the others in hav- 

 ing no transverse processes, in the absence of the anterior 

 zygapophyses, and in having in front a pair of oval, concave 

 facets for articulating with the occipital condyles of the 

 skull. The ninth vertebra has the transverse processes very 

 strong and directed obliquely backward ; it has no posterior 

 zygapophyses, and the posterior surface of the centrum bears 



a pair of prominences 

 for articulation with the 

 urostyle. 



The iirostyle is ele- 

 vated on the dorsal 

 side into a prominent 

 keel which extends 

 nearly to the posterior 

 end. The anterior sur- 

 face possesses a pair 

 of cavities for articula- 

 tion with the ninth 

 vertebra. The verte- 

 bral canal is small and 

 triangular in outline. There is a pair of small openings 

 through the sides of the urostyle near the anterior end for 

 the exit of the last pair of spinal nerves. 



The centra of the vertebrae are joined together by means 

 of pads of hyaline cartilage ; connecting ligaments extend 

 along both the ventral and the dorsal surfaces of the centra ; 

 and the arches and neural spines are joined by .ligaments. 

 The spinal nerves make their exit through the Intervertebral 

 foj-amina, between the sides of the neural arches. 



The Pectoral Girdle and Sternum. — The pectoral girdle 

 is a bony arch which gives support to the fore limbs. The 

 upper end of the girdle is formed by a flat, distally expanded 



s.scp 



SCygf 



Fig. 66. — Transverse section of shoulder 

 girdle, cor, coracoid ; ep.cor, epicoracoid ; 

 gl, gleniod cavity; hu, humerus; sop. scap- 

 ula; s.scp, supra-scapula ; 7^. 3, third ver- 

 tebra. (After Parker and Parker.) 



