PECTORAL GIRDLE AMPHIBIA 



247 



Urodeles (fig. 260) have the cartilage girdle largely persistent, 

 the ossifications in it being small; no membrane bones are present. 

 The scapula is narrow, the precoracoid slender and directed forwards, 

 while the larger coracoid is transverse, there being a large gap 

 (coracoidal fenestra) between coracoid and precoracoid, the median 

 ends of these elements being connected only by ligament, there being 

 no epicoracoid except in Siren and Cryptohranchiis. The median 

 ends of the coracoids overlap as in the Arciferous Anura. The 

 sternum is posterior to the girdle, its anterior border usually grooved 

 to receive the posterior margin of the coracoids. There is usually 

 a cartilage bone in the glenoid region, extending into the scapular 

 part, but its ventral end, which contains the supracoracoid fora- 

 men, is clearly coracoidal. Siren has distinct scapula and coracoid, 

 the upper unossified part of the scapula being usually called a 

 suprascapula. 



Anura have a more typical girdle, scapula, precoracoid and 

 coracoid being present, as is, except in Dactylethra, an epicoracoid 

 (an unossified epicoracoid occurs in the related Pipa). The precora- 



FiG. 261. — Pectoral girdles and sterna of (.4.) Biifo americanus and {B) Rana 

 calesbyana. c, coracoid; cU clavicle; ec, epicoracoid; 0, omosternum; s, scapula; ss, 

 suprascapula; si, sternum; x, xiphisternum. 



coids differ from those of Urodeles in being nearly transverse; 

 the coracoids are more slender and are directed a little backwards. 

 In Arcifera (fig. 261, A) the epicoracoids of the two sides overlap, 

 touching the sternum with their posterior borders. In Firmisterna 

 (fig. 261, B) they abut against the sides of the sternum with which 

 they are intimately associated. Precoracoid, epicoracoid and cora- 

 coid enclose a large coracoid fenestra on either side. 



Ossifications of cartilage are more numerous than in Urodeles. 

 Most of the scapular cartilage forms an osseous scapula, its upper part 



