LACERTA 105 



as streptostylic, see p. 292) ; in connexion with this arrange- 

 ment the upper jaw can be raised relatively to the brain-case. 



The foramen magnum is bounded by the basioccipital, 

 supraoccipital, and exoccipital bones. In front of the basi- 

 occipital, on the floor of the skull, is the basisphenoid, which 

 has a pair of basipterygoid processes for articulation with the 

 pterygoids. In front of the basisphenoid is the parasphenoid. 



On the palatal surface the pterygoids are long bones lying 

 to each side of the middle line. Behind, they connect with the 

 quadrate, their inner surfaces articulate with the basipterygoid 

 processes of the basisphenoid, and in front each pterygoid is 

 connected with two bones : the transpalatine laterally and the 

 palatine medially. The transpalatine is the representative of 

 the ectopterygoid of Gadus. In front of the palatines are the 

 prevomers. The margin of the upper jaw is made by the 

 premaxilla? and maxillas. The ascending process is present 

 and ossified as the epipterygoid, which rises as a slender pillar 

 from the pterygoids. As in other animals, it separates the 

 ophthalmic from the maxillary branches of the trigeminal 

 nerve (see Figs. 138, 148, and 150). 



In the lower jaw, the posterior region of Meckel's cartilage 

 is ossified as the articular ; in addition there are the following 

 membrane-bones : dentary, angular, supra-angular, splenial, 

 and coronoid. Teeth are carried on premaxilla, maxilla, 

 palatine, and dentary. 



The ventral portions of the hyoid and branchial arches form 

 a " hyoid " skeleton beneath the tongue. The hyomandibula 

 is represented by the columella auris, a slender rod which 

 connects the ear-drum or tympanic membrane with the fenestra 

 ovalis in the side of the auditory capsule. This change of 

 function of the hyomandibula from the condition in Scyllium 

 and Gadus, where it supports the quadrate, is made possible 

 by the autostylic method of suspension of the quadrate. 



It is to be noted that the skull articulates with the vertebral 

 column by one median condyle, and that in the formation of 

 the skull, two more segments have been incorporated than in 

 the Amphibia. This accounts for the fact that the hypoglossal 

 nerves emerge from the skull, instead of behind it. 



