OF THE SKULL IK THE COMMON SNAKE. 
399 
A considerable synchondrosis separates the basal centre from the lateral occipital 
patches (eo.) ; these are creeping round the foramen magnum, and show themselves 
on the top (Plate 29, figs. 3-5 ; Plate 30, fig. 1, eo.). 
Each is seen to be perforated for the hypoglassal nerve (12), in front of and within 
the posterior condyloid foramen ( p.c.f. ) ; and they reach to the foramina for the 
glosso-pbaryngeal and vagus (9, 10), which emerge between the ear-capsule and basal 
plate. 
Where the trabeculae pass into that plate — the investing mass — there on their outer 
margin a thin film of bone may be seen (Plate 29, fig. 5, bs.) : these films are the 
symmetrical basisphenoids ; this deposit takes place exactly where the larger para- 
sphenoid of the Bird grafts itself upon the cartilage. 
In some specimens I found a thin ectosteal film over the anterior ampulla (Plate 29, 
fig. 4, pro.) : this is the beginning of the prootic. 
Besides these ossifications, certain changes in the rest of the chondrocranimn have 
to be noticed. 
The small hyoid cartilage now looks downwards and backwards, and the “ tuber- 
culum ” is behind the “ capitulum both are attached to the stapedial plate, and the 
whole structure is cartilaginous : it is the “ columella” ( co .). 
The thin hinder edge of the hyoid is now distinct as a heart-shaped stylo-hyal ( st.h .). 
The alisphenoid (Plate 29, figs. 3 and 5, and Plate 30, fig. 1, al.s.) is now applied 
by its dilated ends to the basal plate, and the concave margins of the two conspire to 
make a large oval foramen for the 5th nerve. 
But the first and second branches, only, pass through this double notch ; the man- 
dibular (third) branch escapes behind the alisphenoid, between it and the prootic 
region of the ear-sac : this lias to do with the backward route it takes in company 
with the lower jaw. 
The 7th or facial nerve passes through the front of the ear-capsule ; close behind 
the third branch of the 5th and a little behind the 7th the 8th nerve enters the 
ear (Plate 30, fig. 1 ; 5, 7, 8). 
The triangular tracts that lie in front of the optic nerve (2, os.) are now becoming 
cartilaginous ; they are the small, free orbito-sphenoids. 
The quadrate hinges on to the articular region of the mandible by a condyle like 
that of the humerus for the ulna ; it forms with it an obtuse and then an acute angle 
(Plate 29, figs. 3, 4, q, ar.). 
The re-entering angle of this joint makes the gape, which is getting further and 
further backwards ; a membrane bone, the squamosal (sq.), intervening between the 
quadrate and the skull. 
The quadrate (q.) is becoming ensheathed with bone ; the upper part, like a Mam- 
malian supra-scapula, and the condyle, being soft. 
On the left side in fig. 4 a rudiment of the pedicle can be seen, but the main part 
at top is the otic process. 
o F 
MDCCCLXXVIII. 
