OF THE SKULL UST THE COMMON SNAKE. 
395 
fibres to the inner walls of the nasal sacs : these sacs have gained their position in 
front. 
The hind brain swells downwards very much, and, like the fore brain of the 
Amphibia, causes the beams of cartilage on which it rests to bend outwards ; we thus 
get a “ posterior basi-cranial fontanelle ” in this type equal to the anterior basi-cranial 
fontanelle (or pituitary space) in the Amphibia (figs. 6 and 8, p.b.c.f). 
The space between the hind and mid brain is now a clean fissure, whose convexity 
is forwards ; it is occupied by a membranous “ tentorium.” 
As in the early stages the mid brain is lifted up on high, and thus the fore and hind 
brains are only separated by the tentorium. 
A membranous floor is now placed beneath the hollow pituitary body. I cannot 
trace any communication between that hollow and the interior of the budding infundi- 
bulum, at present (fig. 5, py., inf.). 
Leaving for awhile the internal structure of the head, we see a very notable out- 
ward form. This may be said to be the Rhyncho saurian stage. 
The earliest condition of my second stage of the Fowl’s head is very similar to this, 
and this is the essential form which is retained in that generalized Lizard, the New 
Zealand Hatteria, and hi the Chelonians generally. 
The head of typical “ Lacertians ” and sub-typical “ Anguians ” (as I shall show in 
future papers) is precisely like the Snake’s head at this stage ; it is the common 
primaeval dragon-form, and is also the fundamental form of the head in “ every winged 
fowl after his kind.” 
The flexure of the head now principally shows itself in the hooking downwards of 
the beak, and the setting of the head on to the arched and hunched neck. 
The nasal sacs occupy a considerable space in front of the brain, their outer and 
inner openings are complete (figs. 3, 4, e.n., i.n.) ; they are roofed by a pair of swelling 
hollow reniform cartilages that he back to back, and are confluent below with the 
confluent fore part of the trabeculae (figs. 5 and 6, ol, tv.). 
We thus have, already, a small septum nasi ( s.n .), which forms an obtuse angle with 
the distinct interorbital tracts of the trabeculae (figs. 5 and 6), and which is terminated 
in front by a hooked flap (figs. 6, 9, c.tr.) ; this flap is formed by the confluence of the 
“cornua trabeculae,” it grows into the fronto-nasal fold, and is, in reality, the rudiment 
(combined into one process) of the foremost visceral arch (Plate 27, figs. 2, 4, 6, n.f.p.). 
In the obtuse angle between this process and the interorbital, free trabeculae, on 
each side of and below the septum nasi, we have the large nasal glands (fig. 5, n.g.) ; 
each gland is enclosed afterwards in two bony capsules — the septo-maxiflary and 
vomer. 
Below the glands and septum there are now well developed pre-palatal folds of skin ; 
the inner nostrils meet behind these and appear as one opening under the fore brain 
(fig. 4, i.n.). 
Above the palatal structures, outside, we have the huge, almost perfect, eye-ball (e.) ; 
