OF THE SKULL IN THE COMMON SNAKE. 
400 
Above the exit of the 12th there is a small passage for a vessel ; this hole is 
evidently the “ foramen condyloideom posticum.” 
In front, on the inner side (Plate 83, fig. 1 ; 5), the large foramen ovale is reniform, 
and the space is large where the Gasserian ganglion gives off the trigemini; but a 
buttress of bone outside (fig. 2), formed by junction of the horns of the alisphenoid 
into a ring, causes the first and second branch to divide off, and leaves the third to take 
a recurrent course. 
This it does (fig. 2 ; 5 3 ) ; and in some Snakes, especially the gigantic kinds, the bone 
is deeply grooved for this large mandibular nerve. 
Behind the foramen ovale there are two larger and one smaller passage ; the first 
of the larger holes transmits the facial nerve (7) ; the largest hole is for the 8th, in 
its passage to the membranous labyrinth. 
A directly lateral view outside (fig. 2) does not show the holes for the 9 th, 10th, and 
12th nerves ; but behind the hole for the facial (7th) we see two rather large passages : 
these are the fenestra ovalis and fenestra rotunda. In the figure the columella (co., st.) 
is dislocated purposely ; it has become relatively small, and its shaft a mere prickle. 
As we saw in the ripe young (Plate 31), two spurs of the opisthotic stand upon the 
edge of the skull floor ; the first of these divides the fenestras from each other, and the 
other forms the back part of the fenestra rotunda, and is clamped to the fore edge 
of the exoccipital. 
In the dry adult skull the fenestra rotunda is seen to have but a slight relationship 
to the membranous labyrinth ; for the cochlear bud does not grow, the stapedial plate 
closes in the passage to the vestibule, and the fenestra rotunda opens into the cavity 
of the skull. 
The lozenge-shaped alisphenoid forms both a wall and an eave to the second part of 
the foramen ovale ; it also forms a double prop on which the swelling prootic rests, the 
“ wing” itself resting obliquely upon its own base — the basisphenoid ( bs .). 
Tins latter is now a compound bone ; it was made from the two proper basi- 
sphenoidal centres, and has gained a bulging floor and a large carinate rostrum from 
the parasphenoid ( pa.s .). 
But neither the parasphenoid nor the basisphenoid directly floor the cranial 
cavity ; the arrest of the chondrocranial elements is correlated with a very curious 
undergrowth of the roof bones (f, p.). 
The frontal meets its fellow below, and the parietal nearly (fig. 1) ; the pituitary 
body is let down through a longitudinal chink between the floor-plates of the parietal, 
and there it finds a large empty room, “ a world too wide” for so small a body. 
By reference to the earlier stages this is easily understood, for the roots of the 
trabeculse were planted on to the “ investing mass” far apart, and no floor existed 
until the parasphenoidal blade grew backwards beneath the unfloorecl space. 
Not only has the front fontanelle, or false floor, thus gained a good floor of bone, 
but the hinder gaping space is floored also (see earlier figures, p.b.cf.). 
3 g 2 
