DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
57 
cavity, is also shown. Meckel’s cartilage (mJc.) is cut off where it is ready to enter 
the Glaserian fissure, and obliquely across the membrana tympani the manubrium 
mallei (m.ml .) runs inwards and forwards, stretching the drum parchment. 
The side view (Plate 6, fig. 6) shows a skull still more in contrast with that of the 
long-faced Edentata than that of the Unau (fig. 3). The simian shortness of the 
face, as compared with the bulk of the swelling skull, is very noteworthy ; for the Ai 
has gone off on one way, as far as the Ant-bear on another.* 
The small snout, with its rounded lateral external nostril (e.n.), surrounded by a 
valvular growth, is followed, in this view, by the maxillary below, and the nasal above 
(mx., n.), for the premaxillary is too small to be seen laterally. 
The short broad nasals (n.) just overlie the facial plate of the short but broad 
maxillary (mx.) ; at the postero-superior angle, however, the frontal ( f ) comes in, and 
below its angle the lacrymal (l.) lies in a notch on the maxillary; it is a small seed¬ 
like bone perforated on its most projecting part ( l.c .). A little below the lacrymal, 
another notch in the hind margin of the maxillary receives the large falcate jugal, which 
forms the lower margin of the orbit. This bone sends downwards a spur behind its 
middle, where it broadens considerably; the free hind part ends opposite the lower 
angle of the parietal (y>.). The bone on the right side (fig. 7) is larger than that on 
the left (fig. 6), and has a deeper and wider descending process ; its postero-superior 
part is also notched in a shallow manner. Even on this side the descending process 
is not equal to that of the embryo Unau (fig. 3, j.). 
Measured along the lower border, the frontal is found to be one-fourth shorter 
than the parietal (f, p.), but the depth of the frontal exceeds that of the parietal on 
account of the large size of its concave orbital plate. The upper fontanelle is not 
quite covered, the lateral membranous space seen in the embryo Unau (fig. 3) is in this 
covered by the meeting together of the frontal, parietal, and squamosal (sq.). 
The large roof-bones are very convex above, their suture—’the coronal—is sinuous, 
the frontal margin being convex above and below and concave in the middle, and the 
parietal the contrary to this. The squamosal, beginning even now to form its large 
air-cavity, forms a roughly oval, convex shell of bone. It has a stout zygomatic 
process, behind and within which is the glenoid facet (gif , see also fig. 5) ; the 
cranial plate runs further forwards than the zygomatic spur, which latter part is 
some distance from the end of the jugal. 
The upper margin of the squamosal, in the large open temporal fossa, is convex, the 
lower is sinuous, dips downwards, and is somewhat notched, behind, where it overlaps 
* If Nature, who “ innovateth gently,” can show us such results as these—can in process of time grow 
the Ai and the Ant-bear from one common “ root-stock ”—we need have no misgivings about the diver¬ 
gence of any primary radical type, whatever. As to sudden variations w'hich may develop into important 
modifications, divaricating this way or that, I shall be able, when I come to the Insectivora, to show 
polymorphic types that suggest possibilities of all sorts. 
MDCCCLXXXV. 
I 
