ANATOMY 03? VERTEBRATES. 



89 



developed from the cxoccipitals, which are separated above and 

 below, as in the Axolotl : each exoccipital forms the posterior half of 

 the otocraue, is perforated by the nervus vagus, and articulates 

 above with the parietal and masto-tympanic. The basisphenoid is 

 very broad and flat : the alisphenoids bound the fore part of the 

 otocraue, transmit the trigeminal nerve, and al^ut against the tym- 

 panic jiedicle in its course backward to the mastoid. The parietals 

 are divided by the sagittal suture and develope a small ridge there 

 posteriorly : each jiarietal sends down a process in front of the ali- 

 sphenoid which rests upon the pterygoid, representing the so-called 

 ' colmncUa' in Lizards. There are no maxillary bones. The alveolar 

 border of the prcmaxillaries, which support a single row of long 

 and slender teeth, ten in mnnber in each bone, terminates in a 

 jioint projecting freely outward and backward. The vomero-])ala- 

 tine bones unite together anteriorly, but diverge posteriorly, where 

 they give attachment liy their outer margin to the pterygoids. 



The two foregoing are examples of the Ichthyomorphs which 

 retain the gills, and thence are termed ' perennilsranchiate.' Tlie 

 Meuopome, figs. 43, 72, and 73, represents a later phase of larval 



72 



Upiier vic-\\' of skull of the Moiiopoiiie. cxxxix. 



UndLl MLV, of IbL bkull. 



life, the gills being absorbed and only the branchial slits re- 

 maining. In fig. 72, e c are cxoccipitals, each developing a 

 condyle ; c, c, parietals ; ff, (j mastotympanics ; /t hypotympanic ; 

 «, a, frontals, h, b, antorbitals ; d, d, nasals ; n, orbitosphenoid ; 

 k, k, prcmaxillaries ; i, i, maxillaries ; /, /, pterygoids. In fig. 

 73, m is the basioccipito-sphenoidal ; e, e, cxoccipitals ; g, y, 

 mastotympanics ; h, h, hypotympanics ; /, /, pterygoids ; /, /, 

 vomers ; k, k, prcmaxillaries. 



In the Frog [Rana) when the metamorphosis is comp)lete, the 



