144 OSTEOLOGY 
THE SKULL AS A WHOLE. 
The skull as a whole may be studied as seen from the front (norma frontalis), 
from the side (norma lateralis), from the back (norma occipitalis), from above 
(norma verticalis), and from below (norma basalis). 
NorMA FRONTALIS. 
In front, the smooth convexity of the frontal bone limits this region above, 
whilst inferiorly, when the lower jaw is disarticulated, the teeth of the upper jaw 
form its lower boundary. The large openings of the orbits are seen on either side ; 
whilst placed mesially and at a somewhat lower level, is the anterior nasal aperture 
(apertura pyriforme), leading into the nasal fosse. 
The frontal region, convex from above downwards and from side to side, is 
limited externally by two ridges, which are the anterior extremities of the temporal 
lines. Superiorly the fulness of the bone blends with the convexity of the vertex. 
Inferiorly the frontal bone forms on either side the arched superior border of the 
orbit (margo supraorbitalis). The space between these borders corresponds to the 
root of the nose, and here are seen the sutures which unite the frontal with the 
nasal bones in the middle line, and with the nasal process of the superior maxilla 
on either side, called the naso-frontal and fronto-maxillary sutures respectively. The 
orbital arch is thin and sharp externally, but becomes thick and more rounded 
towards its inner side, where it forms the internal angular process and unites with 
the frontal process of the superior maxilla and the lachrymal bone on the inner 
wall of the orbit. This arched border is interrupted towards its inner side by 
a notch (incisura supraorbitalis), sometimes converted into a foramen for the 
transmission of the supraorbital nerve and artery. In the middle line, just above 
the naso-frontal suture, there is often the remains of a median suture (sutura 
frontalis), which marks the fusion of the two halves from which the bone is 
primarily ossified. Here also a prominence, of variable extent—the glabella—is met 
with; from this there passes out on either side above and over the orbital margin 
a projection called the superciliary ridge (arcus superciliaris). 
The orbital foss, of more or less conical form, display a tendency to assume 
the shape of four-sided: pyramids by the flattening of the superior, inferior, and 
lateral walls. The base, which is directed forwards and a little outwards, 
corresponds to the orbital aperture. The shape of this is lable to individual and 
racial variations, being nearly circular in the Mongoloid type, whilst it displays a 
more or less quadrangular form in Australoid skulls. The upper margin, as has 
been already stated, is formed by the frontal bone between the internal and external 
angular processes. The outer, and about half the lower, margin are formed by the 
sharp curved edge between the facial and orbital surfaces of the malar bone. The 
internal border and the remainder of the lower margin are determined by the 
outer surface of the frontal process of the superior maxilla, and the sharp edge 
separating the facial from the orbital surface of the same bone. Three sutures 
interrupt the continuity of the orbital margin—the fronto-malar (sutura zygomatico- 
frontalis) externally, the fronto-maxillary (sutura fronto-maxillaris) internally, both 
lying about the same level, and the malo-maxillary (sutura zygomatico-maxillaris) 
inferiorly. The apex of the space is directed backwards and inwards, so that the 
inner walls of the two orbits lie nearly parallel to each other, whilst the outer 
walls are so disposed as to form nearly a right angle with each other. The depth of 
the orbit measures, on an average, about two inches (5 cm.). At the apex there are 
two openings ; the larger, known as the sphenoidal fissure (fissura orbitalis superior), 
passes from the apex of the space outwards and a little upwards for the distance 
of three-quarters of an inch or so, between the roof and outer wall of the orbit. The 
inner third of this fissure is broad and of circular form. Externally it is consider- 
ably reduced in width. Through this the third, fourth, ophthalmic division of the 
fifth, and the sixth nerves enter the orbit, whilst the ophthalmic veins pass 
backwards through it. Above and internal to the inner end of the sphenoidal 
