AMPHIBIA 



203 



first branchial arch. The posterior cornua, which are articu- 

 lated to it posteriorly and are directed backwards on each side 

 of the glottis, are the modified ventral elements of the first 

 branchial arch. All the rest of the branchial apparatus 

 disappears. 1 



The limbs are developed as paired thickenings of the 

 somatopleure mesoderm, and the girdles are developed first. 



The rudiments of the anterior limbs up to the time of 

 metamorphosis remain covered by the opercular fold. The 

 mesodermal thickening grows upwards and downwards in 



Scapula Civ. Cor. 



Omost. Suprascap. 



Sternum 



Xiphisternum 

 Qlenoid cav. 

 FIG. 103. Pectoral girdle from above. After W. K. Parker. 



the body wall and becomes chondrified. The upwardly 

 directed part forms the scapula, and the lower is resolved into 

 two processes the precoracoid and the coracoid. The 

 scapular portion divides into suprascapula and scapula; the 

 former is partially and the latter completely ossified. The 

 lower ends of the two coracoids fuse to form the epicoracoids, 

 and in front and behind paired cartilaginous elements appear 

 which fuse medianly. In front they form the epi- or omo- 

 sternum, which is replaced by bone next the girdle, and 

 posteriorly the elements become resolved into the bony sternum 

 and the cartilaginous xiphisternum. A membrane bone is 

 developed along the anterior border of the precoracoid, and 



1 1897. Ridewood, Proc. Zool Soc. 



