DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 61 
and between the palatine plates of the maxillaries, which together have a convex 
margin outside and a concave margin at the middle, answering to the curved line of 
the fore edge of the palatines. The notch bounding the naso-palatine canal—as seen in 
the skull—is rounded, but each palatine projects a littie where it meets its fellow. 
Outside, the palatines do not form a third of the wall, which is finished by the 
pterygoids (py.); both of these bones are dilated into a subcranial flange above. 
The pterygoids look like short clubs ; they are, in reality, rough shells of bone, and 
open in front into the naso-palatine canal. Being so large, they hide much of the 
alisphenoids, which are clamped by them up to their antero-inferior margin, and are, 
themselves, notched to let the 3rd branch of the 5th nerve (V*.) pass out of the foramen 
ovale. Behind that passage they unite by suture with the squainosal, inside and in front 
of the glenoid facet (g/.f). Along this line of junction with the squamosals the 
pterygoids are grooved; inside that groove they swell into a large bilobate mass, which 
reaches further backwards than the fore edge of the basioccipital (b.0.), close in front 
of the Eustachian openings (ev.). 
Outside the hard palate, in the distance, we see the orbital plates of the frontals 
(7), and nearer the eye, the jugals(j.). These latter bones are large shells, convex 
infero-externally, and concave above ; the inferior margin is cut away in its hinder 
two-fifths, and ends as a free rounded lobe some distance in front of the aborted jugal 
process of the squamosal (sqg.) ; the right Jugal reaches much further backwards than 
the left. This want of facial symmetry I have already described in the Az, also 
(Plate 8, figs. 6, 7,7.). The great extension of the squamosals, fore and aft, is seen in 
this figure, as well as in the side view (fig. 3.) ; for these bones bulge forwards, under 
the parietals, close to the back of the orbit. Hence a considerable tract of each bone 
is seen inside in front of the large uncinate, reniform glenoid facet (g/.f-), with its 
protecting stump of a zygomatic process. Binding obliquely against the side of 
the hinder half of the skull, each bone forms an eave over the tegmen tympani, 
between which and the top of the ear-drum there is a large fissure, the postglenoid 
passage into the pneumatic cavity of the bone (see also fig. 3, sg.). The imperfect 
annulus (a.ty.) surrounding the exposed drum-membrane is fastened, like a horse-shoe, 
under this eave of the temporal bone ; it is less developed than in the A?, but is a strong 
bone notwithstanding.* : 
Outside the palatine, the exposed part of the orbitosphenoid (0.s.) can be seen with 
the optic nerve (II) emerging. Then the alisphenoid, with its special Mammalian 
out-thrust is seen behind the orbital wing and the sphenoidal fissure (V'.) ; close to the 
edge, the foramen rotundum (V®*.) can be seen. Then this thick outstanding wing 
* Many and most instructive parts of the endocranium come into yiew here, and this skull, so lke 
that of the extinct Megatheroids (see Reinwarpr, op. cit.), can be seen to have a most remarkable con- 
formity with that of the great Ant-eater—the little Cycloturus serving as an interpreter between these 
two skulls, whose outward form is so dissimilar. No one, however, who is familiar with the structure of 
Birds—especially the Ratitw, and the Carinate Gralle—will be surprised at this. 
