OF THE SKULL IN THE COMMON SNAKE. 
397 
The form and relations of the ear-sacs are clearly shown in an upper view of the skull 
of the more advanced embryo (fig. 8). 
These large capsules nearly meet above the hind brain, and are separated there by 
a right-angled tract of cartilage, the super-occipital (so.). 
The great size and the alteration of form is due to the rapid growth of the 
semi-circular canals. The two anterior canals ( a.sc .) bound the great fontanelle ; 
each posterior canal ( p.sc .) runs alongside the super-occipital cartilage, and the horizontal 
canal ( h.sc .) bulges outwards over the fenestra ovalis, and forms the outer edge of the 
cranium. 
All the ampullae are outside, but those of the anterior and horizontal canals are close 
together, whilst that of the posterior canal is behind ; the tube of this and of the 
foremost meet above the brain at less than a right angle. 
The chondro- cranium is well developed behind, but dwindles down to almost nothing 
in front of the pituitary body ; distinct filiform trabeculae, and small orbito-sphenoids, 
make up all there is of cartilage in the fore half of the skull. 
The parachordal tracts or investing mass {tv.) are large and united ; they are 
forming the occipital condyle (cc.c.) behind ; have the notochord, short and twisted, 
between and above them in their hinder half, and have a large oval deficiency in front. 
This is what was spoken of just now as the “ posterior basi-cranial fontanelle there 
is a cartilaginous bridge both in front of and behind this space. 
On each side the cartilage grows out into hooked processes, in front of which we 
have the carotid foramen ( i.c .), and the commencement of the trabeculae (tr.). 
The narrow bridge of cartilage which divides the two fontanelles ( p.b.c.f , py. ) 
from each other, is bent forwards ; the pituitary body dips immediately in front of it. 
But, as in Amphibia, the pituitary space is much larger than the pituitary body; it 
is, here, a long spatula in form, with an emarginate blade and a pointed handle. 
This space is bounded by the trabeculae (tr.) and is caused by their form and 
relation ; for from the post-pituitary bridge (which is formed by their apices), and the 
carotid foramina, they run at first outwards, then gently inwards, then they are 
parallel, and lastly they converge, unite, and after a short, free, single tract, they 
become two-crested, and unite also with the descending olfactory laminae (figs. 5, 6, 
8, 9, tr., s.n., ol.). 
The olfactory roofs have already been described ; but before turning to the facial 
rods, I must notice that a long styloid tract of granular tissue is wedged between the 
trabeculae, and reaches the pituitary body by its broad hinder end ; this is the tissue 
which is ready to become the parasphenoid (pa.s.). 
The rudiments of the curious palatal bagket-work are already apparent (fig. 4, 
post-oral arches removed) ; the granular tissue is just ready to develop “ osteoblasts,” 
but no hyaline cartilage precedes the bony tracts that soon appear. 
Two bands on each side unite in front as an arch by means of a key-stone process ; 
this key-stone is the old fronto-nasal process, and continues above the trabecular cornua 
