126 



VERTEBRATE SKELETON 



called sphenethmoids ; but there is some uncertainty here. The 

 columella is usually cartilage through life, but stapedial plate and 

 stylus may ossify separately. The pterygoquadrate is usually 

 ossified in part, but the pterygoid process remains cartilage, a 

 membrane bone (also called pterygoid) developing on its ventral 



Fig. 133. — ,4, Cranium of Amhlysloma ptittctatum; B, of Desniognathus fiiscus 

 (Wiedersheim, 77). eo, exoccipital; /, frontal; /o, fenestra ovale; m, maxilla; w, nasal; 

 OS, orbitosphenoid; p, parietal; pf, prefrontal; pm, premaxilla; ps, parasphenoid; pt, 

 pterygoid; q, quadrate; 5, squamosal; vp, vomero-palatine. 



surface except in Derotremes and those Salamandrines with teeth 

 on the parasphenoid. The quadrate is overlaid by the squamosal, 

 these two, directed downwards and forwards, suspending the lower 

 jaw, the hinge being far forwards, in some species even at the middle 

 of the skull. In some the stylus articulates directly with the quad- 



Fig. 134. — Skull of Proteus (Wiedersheim, '77). bb, basibranchial; ch, ceratohyal; 

 d, dentale; ep, epibranchial; eo, exoccipital; /, frontal; p, parietal; ptn, premaxilla; q, 

 quadrate; sq, squamosal; st, stapes; v, vomer; cartilages stippled. 



rate, an important point in considering stapedial structures as possi- 

 ble homologues of the hyomandibula. 



The roofing bones of the cranium include parietal, frontal, usually 

 nasal, and sometimes a prefrontal (Parker's ectethmoid) on either 

 side, the latter bone forming the anterior border of the orbit. Rarely 

 (Ellipsoglossa, Ranodon, etc.) another bone, now interpreted as 



