OF THE SKULL IN THE COMMON SNAKE. 
393 
thus the rudiments of the 7th and 9th nerves were emerging at a considerable 
distance from each other. 
Now that distance has greatly increased, for the main branch of the facial nerve 
(7th) creeps to the front of the hyoid fold, close behind the hyomandibular cleft ; 
thus the space between these serial nerves is greater than the long diameter of the 
enlarging, egg-shaped ear- capsule. 
This capsule (figs. 3 and 5, au.) is now well covered above with skin ; it is a long 
distance from the eye. 
The eye makes its orbit by nestling in the hollow outside the re-entering angle of 
the crozier-shaped head ; it has no superorbital eave as in the Salmon and the Shark 
for the chondrocranium, which in those types is very massive, is reduced to its 
smallest limits in the Snake. 
The position of the eyeball in front of the maxillary fold will soon be changed ; the 
straightening of the head will throw it over that part. 
At first blush, this stage suggests to the observer that the lachrymal cleft and the 
maxillary fold have their distal ends behind, against the mandibular rudiment. A 
reference to the first stage (fig. 1) corrects this view ; their distal ends are close to the 
nasal pouches. 
These pouches, or inverted cups, are now large and well differentiated, and are 
growing nearer to each other ; between them the leafy folds of the fronto-nasal process 
(first visceral folds) have approximated and united, so that their interspace is a mere 
emargi nation of a single flap (figs. 4 and 6, n. fp ). 
If these cyathiform olfactory rudiments (figs. 3, 4, and 6, ol.) be compared with their 
counterparts in the adult Selachian ( Skate or Shark), their likeness will be at once 
seen. These inverted domes are far apart, the fore brain, growing into hemispheres, 
swelling down between them. 
The crescentic folds that adorn the bottom of these cups, lying concentrically, and 
enclosing towards the inner side lobate masses of cells, do not become transformed 
into the elegant, pectinate membranous turbinals of the Selachian. 
These folds, traced from without inwards, become the septo-maxillary, the two upper 
labials, the nasal gland, and the vomer ; afterwards, these parts crowd towards the 
septum of the nose, and lie below the olfactory region. 
A consistent granular tract, ready to become cartilage, is now formed in the base 
of the membrano-cranium, which is thus breaking into three main layers (besides the 
epidermis), viz., the cutis, the layer of young cartilage, and the dura-mater. 
When the ventral parts of the post-oral folds are cut away, the hind brain severed 
behind its middle, and the head examined from below, we get what is shown in fig. G. 
Besides the best view of the nasal cups and first visceral folds, the floor of the skull 
is better seen. 
In the preparation figured the notochord was severed at its apex, and the granular 
investing mass (parachordal tracts) was cut through the middle. 
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