THE SKULL, FROM IN FRONT (norma facialis) (see fig. t)

This article appears in Volume V25, Page 196 of the Encyclopedia Britannica.

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THE SKULL, FROM IN FRONT (norma facialis) (see fig. t) . The fore-head region is formed by the frontal one, the two halves of which usually unite in the second year; sometimes, however, they fail to do so and then a suture (metopic) may remain to an advanced age. The lower limit of the forehead is formed by the upper margin of the orbit on each side, and by the articulation between the frontal and nasal bones near the mid line. At the junction of the inner and middle third of each supra-orbital margin is the supra-orbital notch for the nerve of that name. Above each supra-orbital margin. is an

elevation

ELEVATION

, better marked in adult males, called the supra-ciliary

ridge

, while between these ridges in the middle line is a slight prominence; the glabella. Below the fore-head the two nasal bones form the skeleton of the upper part of the nose; they articulate with one another in the mid line, but laterally they are joined by a suture to the nasal processes of the maxillae which run up to articulate with the frontal at the internal orbital process, thus forming the inner margin of the orbit.
Externally the malar bones (fig. 1, g) articulate with the frontal at the external orbital process and form the lower and outer quadrant of the orbital margin.
The maxillae or upper jaws (fig. I, M) form the greater part of the skeleton of the face; they complete the lower and inner quadrant of the orbit, and below the nasal bones leave the anterior nasal aperture (apertura pyriformis) between them, and project slightly at the middle of the lower border of this aperture to form the anterior nasal spine. About a quarter of an inch below the infra-orbital margin and just below the articulation with the malar the infra-orbital foramen, for the infra-orbital branch of the fifth nerve, is seen on each side. The lower parts of the maxillae form the alveolar margin in which all the upper teeth are set. Laterally each maxilla is prolonged out into a buttress, the zygomatic process, which sup-ports the malar bone.
Below the maxillae the mandible or lower jaw is seen in perspective (fig. 1, m). The

horizontal

HORIZONTAL

part or

body

BODY

is ,in two halves up to the second year, but after that complete bony union takes place, forming the symphysis. Above the

body

BODY

of the mandible is an alveolar margin containing the sockets of the lower teeth, while below, near the mid line, the bone projects forward to a variable extent and so forms the mental prominence (fig. 1, o), one of the

special

SPECIAL

characteristics of a human skull. Below the second bicuspid tooth on each side is the mental foramen for the exit of the mental branch of the fifth nerve.
The Orbit.Each orbit is a pyramidal cavity, the base of the pyramid being in front, at the orbital margin, and the apex behind, at the optic foramen, where the optic nerve and ophthalmic artery pass through. The four sides of the pyramid form the roof, floor, Inner and outer walls of the orbit. The roof is arched from side to side and is made up of the frontal bone anteriorly, and the lesser wing of the sphenoid posteriorly. The floor is chiefly formed by the maxilla, though the malar forms a little of it in front. There is' a groove for the infra-orbital nerve running forward in it, but before the margin of the orbit is reached the groove becomes a tunnel. The inner

wall

WALL (O. Eng. weal, weall, Mid. Eng. wal, wane, adapted from Lat. vallum, rampart; the
original
- ORIGINAL
O. Eng. word for a wall was wag or tenth)
WALL, RICHARD (1694-1778)

is antero-posterior and parallel with its fellow of theopposite orbit; in front it is formed by the nasal process of the maxilla, behind which the lachrymal bone articulates; together they enclose a vertical groove, for the lachrymal sac, which leads down into the nose, through the naso-lachrymal canal, transmitting the nasal duct (see EvE). Behind the lachrymal bone is the orbital

plate

PLATE

of the ethmoid and in the suture between this and the frontal the anterior and posterior ethmoidal foramina are seen. Posteriorly the ethmoid articulates with the sphenoid, while at its lower and hinder part a small piece of the palate bone comes into the orbit. The outer

wall

WALL (O. Eng. weal, weall, Mid. Eng. wal, wane, adapted from Lat. vallum, rampart; the
original
- ORIGINAL
O. Eng. word for a wall was wag or tenth)
WALL, RICHARD (1694-1778)

of the orbit slopes backward and inward, the two opposite sides therefore converge as they run back. The malar bone, in front, and the

great

GREAT

wing of the sphenoid, behind, form this wall. Between the roof and the outer wail there is a slit in' the posterior part of the orbit called the sphenoidal fissure because it lies between the

great

GREAT

and small wings of the sphenoid ; it transmits the third, fourth, first division of the fifth and

sixth

SIXTH

cranial nerves, as well as the ophthalmic vein.
Another slit called the spheno-maxillary fissure lies in the line of junction of the outer wall and floor, it leads into the spheno-maxillary and zygomatic fossae and transmits the second division of the fifth nerve and some veins.

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