112 COMPARATIVE ANATOMY 



communicates with the pharynx by means of a Eustachian 

 tube. 1 



In most Reptiles a fibro-cartilaginous interorbital system is 

 present (tropibasic character, p. 77), but there is much variation 

 in its development, and the anterior part of the cranial cavity 

 tends to become more or less reduced and shifted dorsalwards. 



On the roof of the skull the parietals usually, and the frontals 

 sometimes, are fused together : a median so-called " parietal 

 foramen " (under Brain) is present in certain recent and fossil 

 forms. The frontals and parietals are either confined to the skull 

 roof, or may also take part in forming its lateral walls. Pre frontals 

 and postfrontals are also present, and there may be a postorbital 

 in addition, as well as a series of supraorbital bones posteriorly to 

 the prefrontal and laterally to the frontal, forming the upper 

 margin of the orbit. Anteriorly to the frontals are, in most cases, 

 a pair of nasals, and laterally to the largely cartilaginous ethmoid 

 region, the lacrymals. 



Anteriorly to the basisphenoid is a paired or unpaired vomer, 

 postero-laterally to which is the palatine, followed by a pterygoid, 

 which may articulate with the basipterygoid process of the basi- 

 sphenoid. Connecting each pterygoid and maxilla in most 

 Reptiles is a so-called transpalatine or ectopterygoid, and in certain 

 forms a rod-like epipterygoid (or antipterygoid) extends in a 

 vertical direction between the parietal and pterygoid, and is 

 comparable to the ascending process of the quadrate in Urodeles. 



The premaxillse, which are in many cases fused together, come 

 into contact with the nasals dorsally and the maxilla laterally: 

 the latter usually bounds the greater part of the gape. A septo- 

 maxillary (p. 98) may be present. Teeth occur in nearly all 

 Reptiles, and may be borne on the palatine and pterygoid, as well 

 as on the premaxilla, maxilla, and dentary. 



The quadrate may be fixed to the surrounding bones, or 

 niovably articulated : the pterygopalatine bar is frequently more 

 or less movable and free from the base of the skull. In some 

 Reptiles its elements become broadened out, and, together with a 

 shelf-like palatine process of the maxilla, may in certain cases 

 even take part in forming a secondary roof to the oral cavity, or 

 hard palate, distinct from the true (sphenoidal) base of the skull. 

 Thus the vomer becomes cut off from the cavity of the mouth and 

 forms a vertical plate situated above the hard palate, and the 

 internal nostrils are thrown further back. 



In the temporal region, typical differences are seen in the 

 various Orders which indicate a very early divergence from the 

 common reptilian ancestor. The bones in this region may form a 

 series of bars, or arcades, separated by spaces or fossce. The main 



1 The form of the columella varies considerably : it consists primarily of a 

 bony rod, to which a cartilaginous extrastapedial is attached distally and applied 

 to the tympanic membrane : both parts are derivatives of the hyoid. 



