DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
237 
bones in a half-ring; these are undoubtedly the progeny of two primary interparietal 
scales that united at the middle and then broke up again in fresh places. There are 
three main pieces, subcrescentic in form; the convexity of the middle piece being in 
front, and of the other two behind ; these are embedded along this wavy line of suture, 
besides several small pieces, like the fragments of the larger tracts. This curious breccia 
is very instructive; the median piece is the proper interparietal ( i.p .), and the main 
lateral pieces (s.t.) are the counterparts of the familiar supernumerary temporal bones, 
or “supratemporals” of the Lacertilia. Bones so situated and so.related are common 
enough in the Gcinoicl Fishes, and in those Teleosteans (Siluroids) that come nearest 
to them in their cranial scutes. 
The side view of this skull is curiously mimetic of that of the Shrew (Plate 31), but 
the teeth are sharply diagnostic. Almost everything is revealed through the thin horn¬ 
like bony walls in this most exquisite little skull ; the roots of the sharp teeth show 
through the outer alveolar wall ; there is no special jugal process beyond the last of 
the series. The maxillary overlaps the frontal above, and then has a round notch 
in which the lachrymal and its canal (l., l.c.) can be seen, although this fine film of 
bone has lost its sutural enclosures. Then there is a sharp spur, under and inside 
which the bone is hollowed out, and becomes a canal for some distance, opening in 
front on a very large infraorbital foramen (V 3 .). Above the sloping postero-superior 
edge of the maxillary, which is parallel with that of the ethmoidal region, a large 
tract of the badly-defined orbit, half its upper, and most of its lower inner face, is 
marked by the rich turbinal folds—middle and upper—of the lateral ethmoids. In 
the middle of their hinder boundary, sloping downwards and backwards, there is a 
large vascular foramen ; and the curled lower edge of the orbital plate of the frontal 
is notched in the middle, below and in front of the larger notch, for the ophthalmic 
nerve (V 1 .). Here, at the postero-interior part of the open orbit, a lobular tract is seen, 
at the bottom of which the orbitosphenoid, pierced by the optic nerve ( o.s ., II.), can 
be seen imperfectly. 
Behind that oblique bony edge, which runs backwards and downwards, and is formed 
by the frontal, in front, the parietal above, and the squamosal behind, the lateral sinus 
( s.c .), throws its exquisite arch, clearly shining through the diaphanous walls of the 
parietal in its temporal region. Half-way between the end of the arch and the supra- 
temporal bone there is a rough vascular foramen, close to the ragged hind edge of the 
parietal. 
The squamosal ( sq .) is about equal to that of the Shrew, but its temporal squama is 
higher, and is lobulate; it is confluent with the parietal in front. 
The thick outer edge forks in front; and in the fork the glenoid facet (yl.c.) lies ; 
the upper fork does not grow forwards as a definite zygomatic process. 
The ribbed outer edge then goes backwards and a little upwards, and then spreads 
into an oblique four-sided enlargement, before it ends, as a sharp spike below the 
