xiv. 5 SKULL 377 



forms is indented to form three partly distinet lobes. In many reptiles 

 there is an epipterygoid bone on either side of the brain-case behind 

 the orbits; this is regarded as an ossification in the ascending process 

 of the palato-quadrate. The lower jaw usually consists of six bones, 

 the articular forming the joint with the quadrate, and the dentary 

 carrying teeth. 



The anterior part of the chondrocranium, surrounding the front of 

 the brain, and the nasal capsule, remain more or less unossified, and 



Fig. 214. Diagram of the skull of lizard to show temporal fossa. 



a. articular; an. angular; bo. basioccipital; bs. basisphenoid; c. coronoid; d. dentary; da. 

 dermal articular; do. dermal supraoccipital; ept. ectopterygoid; eo. exoccipital ; fr. frontal; 

 j. jugal; /. lachrymal; mx. maxilla; n. nostril; na. nasal; o. orbit; op. opisthotic; pa. parietal; 

 pal. palatine; pv. prevomcr; pm. premaxilla; po. post-orbital; pof. post-frontal; pr. pro-otic 

 pra. prearticular; pr}. prefrontal ;ps. presphenoid; pt. pterygoid; q. quadrate; qj. quadrato- 

 jugal; sa. surangular; sf. upper temporal fossa (this is shown diagrammatically, as it occurs 

 in many lizards; in Lacerta it is largely covered by an extension of the post-frontal — see 

 Fig. 213); so. supraoccipital; sp. splenial; sq. squamosal; St. supratemporal; v. vomer. 



(From Goodrich.) 



in places may be membranous. There may, however, be small ossified 

 orbitosphenoids and farther back pleuro- or laterosphenoids, which 

 develop in the pila pro-otica uniting the orbital cartilage with the 

 otic capsules. Between the eyes there is in most reptiles a thin sheet 

 of cartilage known as the interorbital septum, which may be partly 

 ossified by small presphenoid elements. The posterior part of the 

 chondrocranium ossifies to form the following bones; occipital com- 

 plex, basisphenoid, and the ossifications in the otic capsule (pro-otic, 

 opisthotic, &c). 



In many reptiles the upper jaw and front part of the skull can move 

 to some extent in relation to the occipital region and cranial base, 

 such movement being termed kinesis (p. 405). This is often associated 

 with mobility of the quadrate, as in lizards, snakes, and certain dino- 

 saurs. Kinesis helps to widen the gape and may provide a shock- 

 absorbing effect when the jaws are snapped together. 



The postmandibular visceral arches play no part in jaw support but 

 are incorporated into the ear and hyoid apparatus. There is a rod-like 



