74 
MR. W. K. PARKER ON THE STRUCTURE AND 
the manner in which the infero-lateral parts of the endocranium are built upon them. 
Over their junction, and over the exposed part of the pterygoid, the alisphenoid is 
seen, partially, with its foramen ovale (V 3 .) in its middle, far forwards from the primary 
normal place for the escape of the hinder division of the trigeminal nerve.'" 
The squamosal (fig. 3, sq.) is a very narrow, low-lying scale, a lateral or temporal 
scute, differing but little from that of the Frog, but specialized in another manner. 
In that Amphibian the outer or obliquely descending process binds upon a massive 
quadrate region, the hind part of the endoskeletal upper jaw. In this case, that of 
the Mammal, the outer process binds over the much arrested quadrate ( = incus) at its 
proximal part, but the free end acquires a cartilaginous facet for articulation with the 
detached fore part of a compound mandible. The upper edge of the squamosal is 
gently convex, there is a small notch near the end, and the bone then forms a small 
angular process which fits in between the parietal and opisthotic (op.). 
Below that junction, in front of its squared end, the bone is perforated for a vessel; 
it is then lobate, then notched over the front crus of the tympanic ( a.ty .), and, in front, 
on the inside of the short jugal process and glenoid hollow, it ends as a rounded angle 
behind the descending lobe of the parietal (see also figs. 1 and 9). The obliquity of 
the annulus (a.ty.) is well seen here, and the large size of the drum-membrane and 
the manubrium (m.ty., m.rnl.). A convex, roughly pentagonal mastoid region (op.) 
is displayed in this side view, and over it the edge of the huge supraoccipital (s.o.), 
dovetailed by the lateral occipital (o.), behind which the condyle (oc.c.) is hardly 
visible. The projection of the crown of the occipital arch is well shown in this view; 
the general relation and direction of these parts is very similar to what is seen in the 
early embryo of the Unau (Plate 8, fig. 3), whose squamosal (sq.) is probably very 
much like that of the little Anteater at the same stage. In the latter the parietal 
overgrows the squamosal; in the Unau (Plate 8, fig. 3; Plate 10, fig. 3) it is the 
squamosal that becomes so greatly developed, becoming half the size of the parietal, 
whereas in this case it is about one-tenth the sized 
In the Unau, whilst the teeth are thin caps of dentine on small rudimentary pulps 
(Plate 8, fig. 3), the mandibular ramus is not more unlike that of this edentulous type 
(Plate 10, figs. 3, 3a) than it is to that which it will become in the ripe embryo 
(Plate 9, fig. 3). The edge of the ramus is curiously denticulated where the outer and 
inner laminae should form the alveolar walls. This is very similar to what is seen in 
* The position of the foramen ovale in the Mammalia is correlated with many remarkable specializa¬ 
tions that are diagnostic of the skull in this class; one of these is the extreme obliquity, or tilting, of 
the auditory capsules, and another is the out-thrust of the alisphenoids, themselves, which now in the 
Mammal, for the first time, are pushed clean outwards from the general endoskeletal wall. 
f I am satisfied that if a perfect series of embryonic Unaus and Anteaters*—small or large—could be 
obtained, we should find that these two extremely specialized forms of low Eutheria would be found to 
approximate more and more when thus studied clowmvards and backwards; thus they would be seen to 
repeat, in their prenatal state, their secular birth and growth. 
