THE LIZARD. 137 



lower jaw ; a pulley-shaped surface, forming the hinder angle 

 of the inferior temporal fossa, and borne by a curved bone ? 

 the quadrate ( 53). 



38. The basis cranii, a broad plate forming the floor of 

 the brain-case, and continued forwards in the perfect skull 

 by the interorbital septum (Figs. 35 and 37, t.o.s) t a 

 plate of cartilage forming a median vertical partition between 

 the orbits ( 69). 



FIG. 35. Lacerta agilis. Longitudinal vertical section of the 

 skull (after W. K. Parker, slightly altered) X 4. The cartilaginous 

 parts are distinguished by dotting, the membranous spaces by cross- 

 hatching. 



als, alisphenoid : b.o, basioccipital : b.pt, basipferygoid : b.s, basi- 

 sphenoid : e.o, exoccipital : ep.o, epiotic ; e.pt, epipterygoid : fo, fon- 

 tanelle:/r. frontal: i.o.s,, interorbital septum: a, nasal: o.c, occi- 

 pital condyle : op.o, opisthotic : pa, parietal :pa.s, parasphenoid : p.mx, 

 premaxilla : pr.o, prootic : s.mx, septo-maxillary : s.n, septum nasi : 

 s.o, supraoccipital : vo, vomer . I XII, foramina for exit of the cere- 

 bral nerves. 



39. The tympano-eustachian fossa, a depression just 

 external to the basis cranii and bounded by the quadrate : 

 against its dorsal wall lies a small rod of bone, the 

 columella auris ( 65, Fig. 36). 



