254 
MR. W. K. PARKER ON THE STRUCTURE AND 
between the palatine and pterygoid, and blunt behind, where it partly hides the basi- 
sphenoid (b.s.); its front part hides the side of the presphenoid (p.s.) ; it is gently 
arcuate, the convex side being towards the mid-line. To see the rest of the splints 
of the fore part of the skull the palatine plates have to be cut away (Plate 39, fig. 1). 
The main vomer (v.) is five-ninths the length of the wdrole bony skull, measured along 
its base. Its blunt point fits in between the hinder third of the palato-premaxillary 
bars; there it becomes subcarinate, widening gently ; its broadest hinder part is 
distinctly keeled, and that keeled part is exposed in the open nasopalatine passage 
(Plate 37, fig. 1). The subcarinate part is strongly clamped by the bones of the hard 
palate, and thus the nasal passages are divided. The postero-inferior part of the nasal 
labyrinth is underfloored by lateral bones, behind the great inferior openings which 
have the maxillary plates as their floor; but for these plates the greater part of this 
region would be “ schizognathous.” Behind, however, the “ desmognathism ” is 
double—upper and lower ; this is caused by the meeting together of the notched orbital 
plate of the palatines and the “ postero-lateral vomers ” (v ".)—two triangular wedges 
of thin bone that by their most acute angle fit in between the vomer and recurrent 
cartilage in front, have their obtuse angle external, and their less acute angle wedged 
in between the vomer and palatines. These bones are larger than usual for even an 
Insectivore, but are not distinctly Metatherian—as in Rhynchocyon, where they nearly 
meet behind the median vomer. Thus the creature sways, so to speak, everywhere, 
between a normal Eutherian and one of the Metatheria. The strong jugals (j.) 
bind against the maxillaries in front and widen out; they then thicken, are hollow 
outside, and end obtusely just over the glenoid facet ( gl.c .). The great pneumatic 
squamosals (sq.) show some of their most marked characters in this aspect, for both 
the hinge (gl.c.) and the pneumatic cavities are to be seen from below. The zygomatic 
process is short, the glenoid facet is concave, oval, and almost transverse,—it looks 
obliquely downwards, and forwards, and retreats a little at its inner end. The post¬ 
glenoid ridge is large and thick, and the bone extends inwards beyond it, clamping 
the alisphenoid (al.s.), and nearly reaching the cochlea (chi.). The outer edge is 
tucked, as it were, under the skull and round the top of the tympanic cavity. 
Behind, the squamosal embraces the mastoid part of the ear-labyrinth, and that 
edge is, close in front of the arrested and coalesced, epihyal (e.hy.). The roof of the 
tympanic cavity—tegmen tympani — is largely formed by the squamosal, and that 
roof opens into the air-galleries above, that give the sinuous appearance, and apparent 
thickness to the bone (fig. 2, sq.). 
The tympanic ring (a.ty.) is in a remarkable state of development for an embryonic 
Insectivore; its development is equal to that of a Bodent or a Herbivore (Ungulate). 
But although large, the bone is shallow—a mere saucer, and the air cavity in it is very 
limited as to depth; but this is compensated by the extensive galleries that are developed 
in the squamous and mastoid regions (see in the adult, Plate 39). This tympanic 
dish (Plate 37, fig. 1, a.ty.) has a spout in front, an accurate round notch—the 
