696 



PHYLUM CHORDATA : CLASS REPTILIA 



caudal, all the vertebrae are procoelous, as in all living 

 Lacertilians except Geckos, where they are amphicoelous. 



The atlas consists of three separate pieces ; its centrum ossifies as 

 usual as the odontoid process of the axis. There are two sacral verte- 

 bra with large expanded sacral ribs. To the ventral surfaces of many 

 of the caudal vertebra; Y-shaped " chevron " bones are attached. 



pt.o p.e 



pro \ps ' 



oc c 



Fig. 408. — Side view of skull of Lacerta. — After W. K. Parker. 



px., Premaxilla ; mx., maxilla ; /., lachrymal ; j., jugal ; t.pa. 

 transpalatme ; epg., epipterygoid ; pg., pterygoid ; bpg., basi- 

 pterygoid ; b.o., basioccipital ; q., quadrate ; oc.c, occipital 

 condyle; s^., squamosal ; /)r.o., pro-otic ; />^o., postorbital ; st.i 

 st.2, supratemporals ; ps., presphenoid (the optic nerve is seen 

 issumg in front of the end of the reference line) ; p.e mes- 

 ethmoid ; s.ob., supraorbitals; /'/..prefrontal; n., nasal'; ar 

 articular ; ag., angular ; sag., surangular ; cr., coronary ; d ' 

 dentary. ' 



Across the centre of the caudal vertebra? there extends a median 

 unossified zone ; i-t is in this region that separation takes place when a 

 startled lizard loses its tail. 



The ribs are numerous, but only five reach the sternum. 



The skull is well ossified, but in the region of the nares, 

 in the interorbital septum, etc., the primitive cartilaginous 

 brain-box persists, On the dorsal surface the bones exhibit 



