DEVELOPMENT OF THE SKULL IN THE LACERTILIA. 
627 
behind the angle of the mouth the narrowed 1st cleft is seen to be heart-shaped ; a form 
given to it by the “ epi-hyal ” element (columella). 
Behind these parts the 2nd cleft (cl 2 .) is still seen, but this and those behind it are 
fast filling in. 
The relations of the nasal sacs, the huge but unfinished eyeballs, and the auditory 
capsules, will be seen in the sections (Plates 39 and 40). 
The structure of the basal parts of the “ chondrocranium ” will be best understood by 
reference to a basal dissection, and a longitudinally vertical section (Plate 39, figs. 2, 3). 
From below (fig. 2), we see young but solid cartilage forming the basal plate or 
“investing mass” (iv.), and these parachordal bands, as they run forwards, become 
reduced to less than half their width as they pass round the pituitary body ( py.). 
Closing in upon each other in front of that body, these narrow pro-chordal 
trabeculse soon unite for their whole length, and this common bar send upwards 
a cartilaginous crest, the orbito-nasal septum (Plate 39, fig. 3, p.e., s.n.). 
This partition-wall curves downwards in front, and with its upper edge the nasal roofs 
are fused; at the end its base dilates where the cornua unite with the nasal walls. 
On each side of the trabeculae, outside the pituitary space, and in front of the 
Gasserian ganglion (Y) there is a nucleus of cartilage ( b.pg.) for articulation with a 
like cartilage on the pterygoid. 
The notochord lies on the fusing “ parachordal ” bands ; it projects in front of the 
post-pituitary gap, an open space not yet enclosed off from the pituitary space. When 
bounded in front by the “ post-clinoid ” band, it becomes Bathke’s “posterior basi¬ 
cranial fontanelle.” 
The egg-shaped ear-sacs are now invested with cartilage; they rest upon the co¬ 
adapted thin edge of the parachordals (au., iv.), and are coalescing with them. 
The dilated fore end of the coalesced trabeculae shows a tendency to form a visceral 
outgrowth in what was the fronto-nasal process, but it is less distinct than in the 
Snake; moreover, the extensive fusion of, and the long crest upon, the trabeculae, are 
unlike what we see in the Ophidia (“ Snake’s Skull,” Plate 28). 
In conformity with the great size of the eyeball the optic nerve (II) is also very 
large ; it emerges behind a large round notch in the orbital part of the septum, in 
front of the diverging part of the trabeculae, which leaves the floor open for the 
pituitary body. 
That body (py.) is still only grafting itself upon the closed infundibulum; their 
cavities are separate. 
The notochord is seen ascending in front of a thick central mass, the lower part of 
the bulging “medulla oblongata” (C 3 ) ; the cavity of this part of the cerebellum (C 3fl ), 
of the optic lobes (C 2 ), and of the hemispheres (C 1 "), are shown in the vertical section 
(Plate 39, fig. 3). 
Between the fore and mid brain, the “pineal gland” (pi.) is seen, and under and in 
front of the hemispheres, the olfactory crus (I). 
