DEVELOPMENT OF THE SKULL IN TFIE MAMMALIA. 
43 
Inside the glenoid condyle the squamosal runs across and forwards, binding strongly 
on the solid alisphenoids ( al.s.) ; with their help, an oblique thick ridge of bone is 
formed, which runs, with a concave outline, outwards and backwards, from the ptery¬ 
goid to the opisthotic corner of the ear-capsule {op.). There the broad thick basis 
cranii also has a concave margin which runs outwards and backwards, and thus a large, 
oblique, oval space is left in the floor of the cranium ; this is filled in by the auditory 
capsule, mainly by its cochlear region {chi.). On the inside the fissure is filled with 
fibrous tissue until we come to the opening for the vagus and glossopharyngeal nerves 
(X., IX.). In the front of this fissure the internal carotid artery enters. Outside we 
see the higher part of the outer lamina of the squamosal helping to enlarge the tegmen 
tympani, and, in front, the facial nerve (VII.) escapes from the skull, and gains the 
hollow of the tegmen. It then runs along that arched way, and before escaping 
through the stylomastoid foramen burrows through the cartilage formed by the fusion 
of the auditory capsule with the epihyal {e.hy.). 
Near this tunnel, on the side of the capsule, we see the fenestra ovalis ( fs.o .), and at 
the fenestra rotunda (fr.) the outside of the proximal coil of the cochlea {clil.). The 
optic nerve (II.) can be seen emerging from the orbitosphenoid, and behind it an 
oblique tract of the alisplienoid is seen ; it is very thick, has the foramen ovale 
(V 3 .) in its middle, and a suture appears right and left of this hole, due, I have no 
doubt, to a primary division of the bony deposit as in Tatusia, but with the suture 
more oblique. 
Like the other structures, the parachordal region is much more outspread ; the 
basisphenoid {b.s.) has a rounded outline, and does not yet reach the edges of the 
great cartilaginous beam. The basioccipital {b.o.), also, lies in a large tract of 
cartilage, reaching the sides nowhere ; it is oval, with the long diameter median. A 
widish tract of cartilage exists between the basal and lateral bones—the exoccipitals 
(e.o.), on the edge of which, in front, the hole for the hypoglossal (XII.) is seen. The 
unossified capsules, in their opisthotic region {op.), run almost directly inwards, with 
scarcely any paroccipital elevation between them and the condyles {oc.c.). Instead 
of being in front of the general lower face of the skull, the large ovato-reniform 
condyles are behind it, and instead of the supraoccipital tract {s.o.) being largely seen 
in this view, it is only apparent at the hinder outline of the foramen magnum {fm.). 
Hence the setting on of the head in these two types is ver} 7 different; here, it is 
much more terminal than in Tatusia , where it is almost as much under the head as in 
the Primates. On one side of my dissection the ear-drum was left in situ. The 
annulus {a.ty.) is only half as broad as in the other kind, although quite ossified ; a 
considerable space, filled with fibrous tissue, exists between the annulus and the basis 
cranii. The malleus, Meckel’s cartilage, and the membrana tympani {ml., wk., m.ty.) 
are shown in this view, these will be better understood by reference to other figures 
(figs. 3 a and 6). 
The upper view (Plate 7, fig. 2) shows the great breadth and shield-like form of 
G 2 
