DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
191 
above the floor, there being a continuation there of the great pneumatic recess seen, right 
and left, in the hinder two-thirds of the bone. Each recess occupies about half the 
large hinder tract; the inner half is convex, and meets its fellow at the mid-line in a 
deep fissure or sulcus. 
All this wide, spongy, pneumatic structure is merely a peculiar Talpine modification 
of the normal skull of an Insectivore, such as that of the Hedgehog, or the Tenrec. 
The slender zygomatic arch (j.) is finished behind by the squamosal (sq. ) with its 
glenoid facet (gl. c .); this is close outside the tympanic recess of the basisphenoid. A 
character is seen here which is only partly shown on the side view (fig. 4), namely, 
that the squamosal after giving off its zygomatic process, and forming the sinuous plate 
for the glenoid cartilage, grows round and under the skull, strongly clamping and 
binding all the parts by a large squarish postglenoid plate, which grows obliquely 
inwards and a little backwards, and is notched on its inner edge. The two plates, 
right and left, hold the large auditory capsules as in a widely opened vice. 
A considerable tract of cartilage separates the basioccipital ( b.o.) from the car-cap¬ 
sules; it runs backwards, and a little outwards ; it is almost straight, and passes nearly 
into the cartilage of the condyle. Behind the -postglenoid region of the squamosal, and 
to some degree clamped by it, is the large prootic plate ( pr.o.'). In the angle between 
the squamosal and prootic plate (sq., pr.o'.) there is an oblong tract of bone, sub- 
distinct; this is the epiotic (ep.) ; it is bounded within by the hinder part of the 
main opisthotic tract (op.), which has left a considerable tract unossified behind, up to 
the small fusiform cartilaginous paroccipital ridge (p.oc.). In front of that cartilage, 
up to the basisphenoid, there is a large irregular tract of the opisthotic visible below ; 
this is beset with cranial landmarks. Close inside the front lobe of the under part of 
the squamosal the ceratohyal (c.hy.) is seen, tied to the epihyal snag ; behind this 
the facial nerve (VII.) emerges through the stylomastoid foramen. Inside the nerve, 
the hole for the internal carotid may be seen, and behind that, at a good distance, 
the foramen laceriun posterius for the 9th and 10th nerves (IX., X.) is enclosed, 
nearly, by the opisthotic; behind it, over the border, is the hole for the 12th nerve 
(XII.). There is also a crescentic hole under the notch of the squamosal. The use of 
this I did not discover. 
The foramen magnum (frn.) has a neatly egg-shaped outline; in front of it the huge 
basioccipital (b.o.) has a subpentagonal shape. The fore edge is very extensive and 
gently sinuous, for this plate is notched and grooved in front, and this fore edge is 
thick and spongy, answering to the hind part of the basisphenoid. Then, behind 
each thickening, there is a round concavity, from which the bone becomes generally 
gently convex up to the semielliptical notch at the fore part of the foramen magnum. 
A large lozenge-shaped tract of cartilage, pierced on its outside by the hypoglossal 
nerve (XII.), is seen between each postero-lateral edge of the basioccipital and the 
condyles ; these (oc.c.) rise but little in front., and are grooved, crosswise, at their fore 
third, and then on their hinder, narrower part, are more perfectly defined. Wedging 
