58 THE FROG 



are present much as in the adult elasmobranch (see Leuck- 

 art's charts). 



B. The Appendicular Skeleton.- -This consists of the 

 bones of the limbs, and the girdles (pectoral and pelvic) 

 which unite them to the axial skeleton. With the exception 

 of the clavicles, all the bones are cartilage bones. 



i. The pectoral girdle almost completely encircles the 

 body a short distance behind the head. Each lateral half of 

 the pectoral girdle consists of two portions, dorsal and ven- 

 tral, which meet at the shoulder joint. The dorsal ends of 

 the two halves are attached by ligaments and muscles to the 

 vertebral column, while the ventral ends are united together 

 in the median plane by the sternum or "breast-bone." 



(a) The dorsal portion is made up of two parts : 



The scapula, a flat elongated bone somewhat constricted 

 in the middle. The postero-ventral angle forms part of the 

 wall of a cup-shaped cavity, the glenoid fossa, in which the 

 arm articulates. 



The suprascapula is a broad plate of cartilage fastened 

 to the dorsal end of the scapula. When in its natural posi- 

 tion its thin expanded distal end overlaps the second, third 

 and fourth vertebrae. In the adult frog, its proximal portion 

 is calcified and more or less ossified. 



(&) The ventral portion, exclusive of the sternum, is 

 formed of two bars : 



The posterior bar, much stouter than the anterior, is 

 formed by a single bone, the coracoid. Its outer end forms 

 a large part of the glenoid fossa. 



The anterior bar is slender and formed of two elements, 

 clavicle and precoracoid, applied closely together along 

 their entire length. The anterior element, the clavicle, is a 



