PECTORAL GIRDLE. 



271 



In the Urodela the pectoral girdle is mainly cartilaginous 

 being ossified only in the neighbourhood of the glenoid cavity 

 (Fig. 147). The coracoids overlap one another ventrally and 

 are articulated with the anterior end of the sternum. They are 

 without a fenestra, but possess a, well marked precoracoid., 

 There is no clavicle. The radius and ulna are separate and there 

 are usually four and never more than four digits in the manus 

 (3 or 4 in Siren, 3 in Proteus, 2 or 3 in Amphiuma), the pollex 

 probably being absent. The carpus is cartilaginous in the 

 lower and ossified in the higher Urodeles. When four digits 

 are present, it typically consists of a proximal row of three 



FIG. 148. Pectoral girdle and sternum of A, an old male frog (firmisternal), B, an adult 

 female Docidophryne gigantea (arciferous). From Reynolds. In both, the left supra 

 scapula is removed. The unshaded parts are ossified \ the parts marked with small dots 

 are hyaline cartilage, those with large dots calcified cartilage. 1, calcified cartilage of 

 suprascapula ; 2, ossified part of same ; 3, scapula ; 4, coracord ; 5, epicoracoid ; 6, pre- 

 coracoid ; 7, clavicle ; 8, glenoid cavity ; 9, coracoid fenestra ; 10, 11, episternum (omoster- 

 num) ; 12, sternum ; 13, xiphisternum. 



pieces, a distal row of four, and a centrale ; but there is often 

 a certain amount of fusion and suppression of the carpalia 

 and sometimes there is more than one centrale (Megalobatra- 

 chus). 



In the Anura (Fig. 148) the scapular portion of the pectoral 

 girdle is divided into an incompletely ossified suprascapula and 

 an ossified scapula, and the coracoid portion possesses a fenestra 

 dividing it into a cartilaginous, usually slender, precoracoid 

 and a stouter ossified postcoracoid (often called coracoid). The 

 epicoracoid (cartilaginous) is the ventral portion of the coracoid 

 which meets (firmisternal) or overlaps (arciferous, Fig. 148. B) 

 its fellow in the middle line. In the fore-limb the Radius and 

 ulna are fused, the carpus is usually reduced, and there are four 



