116 COMPARATIVE ANATOMY 



the hyoid, the latter consisting of a body (basi-hyobranchial) and 

 of two pairs of cornna. 



Lacertilia (Figs. 80 and 82). There is an interorbital septum 

 except in the Amphisbsenidse, and in it there may be indications 

 of orbitosphenoids or alisphenoids : the orbit is usually separated 

 from the temporal fossa. Various modifications are seen as 

 regards the temporal arcades, but an inferior arcade, or lower 

 zygoma, is never present. 1 The quadrate is in most cases movably 

 articulated to the distal end of a parotic process from the temporal 

 region. There is a " parietal foramen " (situated in the frontal 

 region in Chameleons) ; the parietals are usually fused, and the 

 frontals may also become united in the adult. Lacrymals are 

 generally present, and epipterygoids occur except, e.g. in Amphis- 

 bsenians and Chameleons. The pterygoid is movably articulated 

 to the quadrate and basipterygoid process of the basisphenoid, 

 and there is a basisphenoidal rostrum. The premaxillae are usually 

 fused. Teeth occur on the premaxilla, maxilla, dentary, and 

 frequently also on the palatine. 



The hyobranchial skeleton (Fig. 80, c) consists of a narrow 

 basal portion extending forwards into the tongue, from which three 

 pairs of cornua may arise, belonging respectively to the hyoid and 

 branchial arches 1 and 2. 



Ophidia (Fig. 83). The embryonic chondrocranium is much 

 less extensive than in Lizards. In the orbito-temporal region, there 

 is hardly any cartilage, the parietals and frontals forming lateral 

 walls to the cranium, which extends to the ethmoid region, and 

 even here the amount of cartilage is small. The trabeculae remain 

 separate for the greater part of their length, forming narrow rods 

 lying side by side, which in many cases can be recognised even in 

 the adult. The skull, however, is here also of the tropibasic type 

 (p. 77) : a thin interorbital septum is developed, but is compara- 

 tively little marked and does not become chondrified. There is a 

 large parasphenoidal rostrum on the basisphenoid, the parietals 

 are united, and there are no temporal arcades or supratemporal 

 bones. The great strength and solidity of the investing bones is 

 doubtless correlated with the modifications of the jaws in con- 

 nection with the mode of feeding. 



In most Snakes, the quadrate is only indirectly connected with 

 the skull by means of the squamosal, with the distal end of which 

 it articulates and which extends backwards, thus resulting in a 

 very wide gape ; moreover, the facial bones are capable of move- 

 ment upon one another and upon the cranium. The pterygoid 

 articulates posteriorly with the quadrate without the intervention 

 of a jugal. The premaxilla is impaired and usually edentulous 

 (except, e.g. in Pythons). The rami of the mandible are connected 



1 In Chameleons, characteristic processes arise from the cranial roof and 

 temporal regions, and unite above the posterior part of the skull in the median 

 line. 



