DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 181 
the basal region swells out into broad hips which end, behind, in the slightly convex 
but very large condyles (0c.c.); these are wedge-shaped and have a sulcus across them 
at their front third, they are almost pointed behind, when they reach nearly to the 
end of the enormous foramen magnum (f.m.), the fore part of which is a semicircle, 
whilst the hind part widens out irregularly. The fore margin of each condyle is gently 
emarginate. 
The hinder or opisthotic region of each large auditory capsule is completely con- 
fluent with the corresponding side of the occipital arch ; the paroccipital region is a 
mere gentle convexity. The exoccipitals (c.o.) can be seen outside the condyles as 
narrow tracts of endosteal bone; the supraoccipital (s.o.) reaches the top of the 
foramen magnum. 
Outside the front part of the condyle (oc.c.), the condyloid foramen (XII.) is seen, 
the 9th and 10th nerves (IX., X.) are seen in the distinct foramen lacerum 
posterius, and the facial nerve (VIi.) is visible in this view, emerging from the f. 
stylomastoideum, behind the epihyal (e.y.). The uppermost part of the hyoid arch— 
the stapes (st.)—is shown, i situ, on the right side of the figure, and the incus and 
malleus, with a part of Meckev’s cartilage (¢., m/., mk.) on the other side. The 
“otic process” or short crus of the incus or quadrate—a secondary retral part of the 
suspensorium of the mandible in the Ovipara, and which in them often reaches 
beyond the auditory capsule to join the occipital arch—is here seen to be in front of 
the semicircular canals. Both the mandibular elements of the ear-chain lie, now, in a 
large vacuity of the chondrocranium, which is caused by the curious non-development 
of the alisphenoid at that part. All round the pupiform cochlea (ch/.) the line of 
separation of the capsules and chondrocranium, proper, is perfect ; and again, on the 
outside, the opening into the lateral sinus (/.s.) marks off the epiotic region from the 
supraoccipital cartilage ; but in front of the sinus-opening, laterally (fig. 3), and along 
the paroccipital region (fig. 5), the confluence of the two structures has been complete. 
The fenestra ovalis is filled by the stapes (st.), the fenestra rotunda (/7.) is seen 
on both sides. 
In the /ateral view (fig. 3), the supraoccipital, supra-auditory, and posterior 
orbitosphenoidal tracts of cartilage (s.0., s.a.c., 0.s.), are seen to be confluent, and the 
whole hind part of the skull, strongly bent downwards, is composed either of cartilage 
or of cartilage-boue (endostosis). Over the foramen magnum the supraoccipital is 
large, both high and wide, and the exoccipital (e.0.), is seen to be wider than the 
lower view would indicate. There is no appearance of bone in the auditory capsule, 
except over the front part of the anterior canal (a.s.c.), and the sinus-opening ; the 
labyrinthic part of the capsule is still cartilaginous. ‘The oblique oblongo-crescentic 
tract of bone seen, already, in the sphenotic and pterotic regions, is the first of the two 
bony periotics formed in the auditory capsule in this type; notwithstanding its 
growth along the crest of the capsule, and the fact that it does not help to enclose 
the labyrinth, I consider it to be the “ prootic,” and the other, formed afterwards, 
the “ opisthotic.” 
