DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
203 
is, in the Shrews, very long and very slender, it runs backwards and a little inwards. 
Some parts of the endoskeleton are best seen in this outer side view; especially the 
prootic plate ( pr.o'.) and the proper mastoid region. The prootic plate, which takes the 
work here of the “sphenotic and pterotic” of Fishes, and does but little of its own, is a 
large shield-shaped ossification of the supra-auditory region of the cartilaginous endo- 
cranium. Its arched top does not yet reach the emargination in the parietal, nor 
the lateral sinus (s.c.), which now forms an elegant bow over the side skull, inside 
the parietal for the most part, but exposed, behind. The roughly dentate lower 
hinder edge of the prootic plate overlaps the ampulla of the anterior canal ( a.s.c.) and 
in some degree that of the horizontal canal ( h.s.c.) ; then this bone meets with the very 
extensive opisthotic (at h.s.c.). That bone can be seen behind the tympanic ( ct.ty .), and 
also creeping over the junction of the anterior and posterior canals (a.s.c.,p.s.c.); much 
of that part of the capsule (epiotic region) is still cartilaginous ; there is no appearance 
of a distinct epiotic bony centre. Part of the interparietal (i.p.) is seen in front of the 
supraoccipital (s.o.), and the occipital arch is seen edge-wise ; there is still cartilage 
between the supra- and exoccipitals (e.o.) and the latter run up to the auditory capsule, 
without forming any definite paroccipital process ; the condyle ( oc.c.) is very large, and 
looks obliquely downwards and outwards. The whole hind skull is gently convex and 
very similar to that of the Mole, with which it agrees in having the large prootic plate. 
The lower view (Plate 29, fig. 2) shows the large alveolar grooves, overfull of tooth- 
pulps, with cusps cutting the gums ; thus the marginal part of the premaxillaries (px.) 
as well as of the maxillaries (mx.) is very wide and bulbous, The palatine processes 
of the premaxillaries are very long and slender, and continuous with each anterior 
paired vomer, right and left. The palatine plate of the maxillaries is large, and twice 
the extent of that of the palatines (pa.) ; the suture between these four plates is 
arched forwards, and the fore margin of each palatine is deeply notched ; there the 
anterior palatine foramen is open in front. 
The merely vertical and upper part of the palatines is short and swollen, and the 
similar tracts formed by the pterygoids (pg.) are swollen also; the hamular processes 
are small, but sharp; they have used up the primary cartilaginous nucleus. Of the 
other investing bones to be seen in this aspect the squamosals (sq.) are the most 
striking; they are much larger than they seem to be from the side view, being curled 
round under the side of the skull in a remarkable manner. The postglenoid region is 
very large; the preglenoid a short free spike; the glenoid facet (gl.c.) looks forwards 
and a little inwards, and is, at present, a continuous selliform facet to the wide, thick 
infero-anterior lobe of the bone. Inside the hinder portion of the squamosal, the 
annulus tympanicus (a.ty.) is seen as a relatively large, very thin, imperfect ring of 
bone, bending upon the emerging primary mandible— Meckel’s cartilage {ink .)—and 
supporting a wide membrana tympani (m.ty.) ; the hinder crus has a widened part or 
blade at its free end, and the fore end is dilated, but to a less degree. The vomer (v.) 
is seen in its hind part, with its forks, supporting the perpendicular ethmoid (p.e.). 
2 D 2 
