410 
MR. W. K. PARKER ON THE STRUCTURE AND DEVELOPMENT 
Now, (Plate 32, fig. 2, bo., bs, and Plate 33, figs. 1, 2, bo., bs .) tlie basioccipital and 
the basisphenoidal plates have supplied what was wanting by periosteal growths ; 
between these two large slabs there is a persistent spheno -occipital suture. 
The post-pituitary part of the basisphenoid (Plate 33, fig. 1, bs.) shelves down 
behind the post-clinoid ridge, obliquely roofing the sub-cranial cellar ; this it does 
completely, behind. 
But in front, as before said, the two parietals fail to meet below the mid brain 
(fig. 1) ; they, however, send strong tentorial ingrowths, which run from the front of 
the auditory mass into the floor. 
Above (Plate 32, fig. 1, p.), the parietals are completely confluent along the sagittal 
line ; there they are somewhat depressed in this small kind, but in the gigantic kinds 
there is a parietal crest as strong as that of the ITysena or the Tiger. 
Also behind the coronal suture (which is persistent) the parietal grows inwards, 
filling up the space above, between the mid and fore brain (Plate 33, fig. 1, p.). 
Above the beginning of the rostral part of the sphenoidal beam there is a large 
optic fenestra, as in the Batrachia, much larger than the optic nerve, and above this 
there is a post- orbital fenestra between the orbital regions of the parietal and frontal 
(Plate 33, figs. 1 and 2). 
Tins is partly filled in by the small trifoliate orbito-sphenoid (os), which cleaves to 
the hind edge of the frontal descending plate. 
The parasphenoidal rostrum ascends to meet the orbito-sphenoid in the angle between 
the diverging optic nerves, then for the rest of its length the crest is lower (Plate 33, 
figs. 1, 2, 3, pa.s.). 
Both externally (fig. 2) and in section (fig. 3) the trabeculae (tr.) are seen as unossified 
rounded rods, as far as the parasphenoid goes, that is, up to the olfactory region. 
As in front of the ear -mass the parietals grew inwards, so behind the olfactory walls 
the frontals do also, but more perfectly (Plate 33, figs. 1 and 4, f.), for they are fitted, 
face to face, at the mid-line. 
A recess on each side receives the narrow end of the fore brain, and under these lobes 
(C 1 ) the olfactory crura (1) pass to their destination (fig. 4). 
There the frontals spread and articulate with each prefronto-lachrymal ( pf ), but 
further back they completely enclose the brain, as in certain Mammals (Plate 33, 
% 3,/). 
The sectional view (fig. 3) shows well the curious architecture of the Snake’s skull : 
the roof and side walls are made by the frontals, the former flat, the latter concave 
and slanting inwards; the frontal suture (Plate 32, fig. 1 ,f) is persistent. An eave 
is formed by the prefronto-lachrymals (pf), and a strong foundation by the crested 
parasphenoid (pa.s.), burrowed on each side by the trabeculae (tr .) : here the whole 
strength of this strong building is derived from membranous materials external to the 
endo-cranial elements. 
The post-orbital region has an additional eave-tile, a post-orbital scale bone (pt.o.), 
