THE LIZARD. 143 



and below the fenestra ovalis, and serving for the passage 

 of the Qth, loth, and nth cerebral nerves: the i2th 

 nerve makes its exit by two small condylar foramina in 

 the posterior part of the exoccipital (XII). 



67. A notch (V) in the anterior border of the prootic, 

 converted into a foramen in the complete skull by the 

 membranous side-walls of the anterior moiety of the brain- 

 case ( 69) ; it transmits the 5th and 7th nerves : behind 

 and below it and also in the prootic is the internal 

 auditory meatus for the exit of the 8th nerve (VIII). 



VI. The foregoing sections, with the exception of the part of 65 

 in small type, can be made out on the dried skull : for the 

 following sections prepare a second skull with great care, 

 giving special attention to the preservation of the interorbital 

 septum : boil it in water for a few minutes, and then carefully 

 remove the roofing bones, the premaxilla, maxilla, vomers, 

 palatines, transpalatines, and pterygoids : note 



68. By the removal of the above-mentioned membrane-bones, the 

 primordial skull or chondrocranium (Fig. 37) is left, and is seen 

 to consist of cartilage containing certain endogenous ossifications or 

 cartilage bones, namely the basi-, ex-, and supraoccipital, the basi- 

 sphenoid, and the pro-, epi-, and opisthotic. 



69. The interorbital septum (Figs. 35, 37. i.o.s), a median vertical 

 plate of cartilage continued forwards from the anterior border of the 

 basisphenoid to the junction of the palatines and vomers, whence it 

 further extends as the septum nasi (s.n) to the end of the snout, 

 forming the partition between the nasal sacs ; the dorsal edge of the 

 interorbital septum closely underlies the anterior part of the brain, 

 and gives off, on each side, a partly cartilaginous partly membranous 

 plate, directed upwards and outwards, which, uniting behind with the 

 prootic, above with the skull roof, and in front with the descending 

 processes of the frontals, furnishes a side-wall to the anterior part 

 of the brain-case : the interorbital septum and its wings have in trans- 

 verse section the form of a Y. Paired ossifications in the posterior part 

 of the membrane-cartilaginous skull walls representthe alisphenoids (al.s). 



70. The nasal capsules (Fig. 37, na), rounded cartilaginous enclo- 

 sures, lying one on either side of the septum nasi, of which they are lateral 

 developments ; each consists of a roof which springs from the dorsal edge 



