160 OSTEOLOGY. 



The Skull from the Front (Norma Frontalis). 



In front, the smooth convexity of the frontal bone limits this region above 

 whilst inferior ly, when the lower jaw is disarticulated, the teeth of the maxilla 

 form its lower boundary. The large openings of the orbits are seen on either side 

 whilst placed centrally, and at a somewhat lower level, is the apertura piriformij 

 (anterior nasal aperture) leading into the nasal cavity. 



The frontal region, convex from above downwards and from side to side, if 

 limited laterally 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 each 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 medially, and with the frontal process of the maxilla or 

 each side, called the naso-frontal and fronto-maxillary sutures, respectively. The 

 supra-orbital margin is thin and sharp laterally, but becomes thick and more 

 rounded towards its medial end, where it forms the medial angular process ant, 

 unites with the frontal process of the maxilla and the lacrimal bone in th( 

 medial wall of the orbit. This arched border is interrupted towards the media! 

 side by a notch (incisura supraorbitalis), sometimes converted into a foramen, foi 

 the transmission of the supra-orbital nerve and artery. In the median plane, jusl 

 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 bom 

 is primarily ossified. Here also a prominence, of variable extent the glabella if 

 met with; from this there passes out on each side above and over the orbita 

 margin a projection called the superciliary arch. 



The orbital fossae, of more or less conical form, display a tendency to assuim 

 the shape of four-sided pyramids by the flattening of the superior, inferior, anc 

 lateral walls. The base, which is directed forwards and a little laterally 

 corresponds to the orbital aperture. The shape of this is liable to individual anc 

 racial variations, being nearly circular in the Mongoloid type, whilst it displays i 

 more or less quadrangular form in Australoid skulls. The superior margin, at 

 has been already stated, is formed by the frontal bone between the zygomatic anc 

 medial angular processes. The lateral and about half the inferior margins arc 

 formed by the sharp curved edge between the facial and orbital surfaces of the; 

 zygomatic bone. The medial border and the remainder of the inferior margir 

 are determined by the lateral surface of the frontal process of the maxilla, anc 

 the sharp edge separating the facial from the orbital surface of the same bone 

 Three sutures interrupt the continuity of the orbital margin zygomatico-fronta: 

 laterally, the fronto-maxillary medially, both lying about the same level, and th( 

 zygomatico-maxillary inferiorly. The apex of the space is directed backwards anc 

 medially, so that the medial walls of the two orbits lie nearly parallel to eacl 

 other, whilst the lateral walls are so disposed as to form almost a right angle witl; 

 each other. The depth of the orbit measures, on an average, about two inche.' 

 (5 cm.). At the apex there are two openings ; the larger, known as the superio] 

 orbital fissure (O.T. sphenoidal), passes from the apex of the space laterally and * 

 little upwards for the distance of three-quarters of an inch or so, between th< 

 roof and lateral wall of the orbit. The medial third of this fissure is broad anc 

 of circular form. Laterally it is considerably reduced in width. Through this 

 the oculomotor, trochlear, ophthalmic division of the trigeminal, and the abducent 

 nerves enter the orbit, whilst the ophthalmic veins pass backwards through it 

 Above and medial to the medial end of the sphenoidal fissure there is a smalle: 

 circular opening, the optic foramen, for the transmission of the optic nerve anc 

 ophthalmic artery. 



The roof of the orbit, which is very thin and brittle towards its centre 

 is formed in front by the orbital part of the frontal bone, and behind by ; 

 small triangular piece of the small wing of the sphenoid, which surrounds th< 

 optic foramen and forms the upper border of the superior orbital fissure. Laterally 



