DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
213 
The interparietal is small for an Insectivore, but the true supraoccipital (s.o.) is 
unusually large, and suggests at once a Monotrematous relationship. The thrice- 
convex hind margin is wide, but the fore edge runs across the skull to the post- 
temporal region, and is nearly as wide as the two parietals, together, at their widest 
part. Moreover, the tract covered by the supraoccipital tegmen is almost as extensive 
as that which is covered by the frontals. 
In the side view (Plate 19, fig. 3) the peculiarities of the Soricine skull are well 
shown; a Mammalian skull, truly, but reduced to its utmost tenuity. There is a 
general parallelism in the downward and forward curve of the various parts ; the 
snout also is thus followed by the premaxillaries (px.), with their notched and ferru¬ 
ginous teeth—like the mandibles of a Beetle—and the elements of the skull, further 
back, dip in front, in like manner. 
Back, as far as to the coronal and squamous sutures, which are largely persistent, 
there is no sign, in this view, of composition; the badly formed orbit has the frontal 
coming well down on its inside, but it merely dips inwards a little, it forms no brow ; 
nor is there any definite post- or preorbital wall or outwork. 
For such a snout the maxillary nerve (V 2 .) has to be very large, for the lips are 
thick, and the vibrissce well developed; the canal, therefore, is very large, and it is 
perfected by the maxillary, which has a stump of bone in the jugal region ; the canal- 
wall for the infraorbital nerve is itself perforated. The lachrymal (/.) is melted into 
the fore edge of the maxillary, and the sphenoidal wings, front and hinder (o.s., al.s.), 
are all confluent with the overlying membrane-bones; so also are the palatine bony 
tracts with the bones above them. In the inner and lower face of the undefined orbit, 
the sphenoidal fissure (II., V 1,3 .) is seen as a large channel, opening obliquely; this is 
> due to the fact that the alisphenoid (al.s.) embraces the orbitosphenoid (o.s.), growing 
freely outside it. 
The curious, low-lying, oblong squamosal (sq.) opens in front as two short blunt 
blades, which seem to bite the outspread alisphenoid ; this is due to the fact that, 
whilst the jugal process is aborted and has no jugal bone to lie upon, the condyle 
(glenoid cavity) has become subdivided into two tracts of articular cartilage, one 
above and one below. Thus the two-faced condyloid head of the lower jaw 
(figs. 3, 4, cd.p.) is really held between the two blades of the squamosal. In the 
crescentic hollow behind these blades the normal pneumatic foramen is seen; the bone 
there is narrower, then broadens somewhat, and then, dipping gently, ends as a rounded 
or ear-shaped lobe in the re-entering angle formed by theprootic plate (pr.o'.), and the 
mastoid region of the ear capsule (op.). Under its concave edge—greatly turned 
inwards (see fig. 2, sq.) —the tympanic (a.ty.) can just be seen. The structure of the 
skull in the temporal region is very elegant; the larger hind skidl is finished by the 
large parietals (p.), which imbricate the frontals in the postorbital region, and throw 
themselves backwards and downwards, over the hinder auditory region, clamping all 
the parts with their toothed edge. They come down with a straight edge to the 
