SKULL — AMPHIBIA 



^33 



The roof of the mouth, which has a large vacuity on either side, 

 is most formed by a large parasphenoid, the first bone to ossify in 

 the skull. It is expanded behind, a process extending to either 

 otic region; its anterior end covers part of the ethmoid, and on 

 either side of its tip is a slender palatine bone in a transverse position, 



Fig. 142. — Dorsal and ventral sides of skull of Rana calesbiana. e. ethmoid; eo, 

 exoccipital; //>, frontoparietal; _/', quadratojugal; mx, maxilla; n, nasal; p, palatine; pin, 

 premaxilla; po, prootic; pq, pterygoid overlying pterygoquadrate; ps, parasphenoid; 

 q, quadrate cartilage; s, squamosal. 



reaching to maxilla and pterygoid. The toothed vomers in front 

 of the palatine are small. As in other Tetrapoda the pterygoid 

 bones are membranous in origin. Each reaches the maxilla and 

 palatine in front; one of its posterior processes extends to the para- 



FiG. 143. — Development of hyobranchial apparatus of Rana (Stohr, '81, and Gaupp, 

 '05). A, 9 mm. larva; B, 29 mm. larva; C, end of metamorphosis; D, adult (Gaupp, 

 ■96). ac, anterior cornu; b, branchial arches; c, copula; cb, ceratobranchial; ch, body of 

 hyoid; h, hyale; he, hyoid cornu; th, 'thyreoid process.' 



itral side of the 



sphenoid, the other runs postero-laterally on the ventiai si^c wi unc 

 quadrate, parallel to one of its branches. 



The suspensor of the lower jaw, formed of quadrate, squamosal 

 and pterygoid, is directed backwards and downwards, carrying the 



