ANATOMY OF VEKTEBRATES. 



89 



developed from the exoccipitals, which are separated above and 

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

 the otocrane, 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 

 otocrane, transmit the trigeminal nerve, and abut against the tym- 

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

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

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

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

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

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

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

 point projecting freely outward and backward. The vomero-pala- 

 tine bones unite together anteriorly, but diverge posteriorly, where 

 they give attachment by their outer margin to the pterygoids. 



The two foregoing are examples of the Ichthyomorphs which 

 retain the gills, and thence are termed ' perennibranchiate.' The 

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



Upper view of skull of the Menopome. cxxxix. 



Under view of the skull. 



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

 maining. In fig. 72, e e are exoccipitals, each developing a 

 condyle ; c, c, parietals ; g, g mastotympanics ; h hypotympanic ; 

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

 k, k, premaxillaries ; i, i, maxillaries ; /, f, pterygoids. In fio-. 

 73, m is the basioccipito-sphenoidal ; e, e, exoccipitals ; g, g, 

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

 vomers ; k, k, premaxillaries. 



In the Frog (Rana) when the metamorphosis is complete, the 



