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Part I. where the glandula innominata Galeni, or lachrymalis, is lodged.—Behind each internal angular process, a small pit may be remarked, where the cartilaginous pully of the musculus obliquus major of the eye is fixed.—Betwixt the two orbitar processes, there is a large discontinuation of the bone, into which the cribriform part of the os ethmoides is incased.—The frontal bone frequently has little caverns formed in it here where it is joined to the ethmoid bone.—Behind each external angular process, the surface of the frontal bone is considerably depressed where part of the temporal muscle is placed.

The foramina, or holes, observable on the external surface of the frontal bone, are three in each side.—One in each superciliary ridge, a little removed from its middle towards the nose; through which a twig of the ophthalmic branch of the fifth pair of nerves passes out of the orbit, with a small artery, from the internal carotid, to be distributed to the teguments and muscles of the forehead.—These vessels in some sculls make furrows in the os frontis, especially in the bones of children; and therefore we ought to beware of transverse incisions on either side of the os frontis, which might either open these vessels or hurt the nerves, while they are yet in part within the bone; for, when vessels are thus wounded, it is difficult to stop the hæmorrhagy, because the adhesion of a part of the artery to the bone hinders its contraction, and consequently styptics can have little effect; the sides of the furrow keep off compressing substances from the artery; and we would wish to shun cauteries or escharotics, because they make the bone carious; and nerves, when thus hurt, sometimes produce violent symptoms.-But we must remark, that often, instead of a hole, a notch only is to be seen: Nay, in some skulls, scarce a vestige even of this is left; in others, both hole and notch are observable, when the nerve and artery run separately. Frequently a hole is found on one side, and a notch on the other; at other times we see two holes; or there is a common hole without, and two distinct entries internally. Near the middle of the inside of each orbit, hard by, or in the transverse suture, there is a small hole for the passage of the nasal twig of the first branch of the fifth pair of nerves, and of a branch of the ophthalmic artery. This hole is sometimes entirely formed in the os frontis; in other skulls, the sides of it are composed of this last bone, and of the os planum. It is commonly known by the name of orbitarium internum, though anterius should be added, because of the next, which is commonly omitted.—This, which may be called orbitarium internum posterius, is such another as the former; only smaller, and about an inch deeper in the orbit: through it a small branch of the ocular artery passes to the nose.—Besides these six, there are a great number of small holes observable on the outer surface of this bone, particularly in the two protuberances above the eye-brows. Most of these penetrate no further than the sinuses, or than the diploe, if the sinuses are wanting. The place, size, and number of them, are however uncertain: They generally serve for the transmission of small arteries or nerves.

The internal surface of the os frontis is concave, except at the orbitar processes, which are convex, to support the anterior lobes of the brain. This surface is not so smooth as the external; for the larger branches of the arteries of the dura mater make sonic furrows in its sides and back-parts. The sinuosities from the luxuriant risings of the brain, mentioned when describing the general structure of the cranium, are often very observable on its upper part; and its lower and fore parts are marked with the contorsions of the anterior lobes of the brain.—Through the middle of this internal surface, where always in children, and sometimes in old people, the bone is divided, either a ridge stands out, to which the upper edge of the falx is fastened, or a furrow runs, in which the upper side of the superior longitudinal sinus is lodged; on both these accounts chirurgical authors justly discharge the application of the trepan here.

Immediately at the root of this ridge or furrow there is a small hole, which sometimes pierces through the first table, and, in other skulls, opens into the superior sinus of the ethmoid bone within the nose. In it a little process of the falx is lodged, and a small artery, and some times a vein, runs; and the superior longitudinal sinus begins here.—This hole, however, is often not entirely proper to the os frontis; for in several skulls, the lower part of it is formed in the upper part of the base of the crista galli, which is a process of the ethmoid bone.

The os frontis is composed of two tables, and an intermediate diploe, as the other bones of the cranium are, and in a middle degree of thickness between the os occipitis and the parietal bones.

The diploe is also exhausted in that part above the eye-brows, where the two tables of the bone separate, by the external being protruded outwards, to form two large cavities, called sinus frontales.—These are divided by a middle perpendicular bony partition.—In some skulls, besides the large perpendicular septum, there are several bony pillars, or short partitions, found in each sinus; in others these are wanting.—For the most part the septum is entire; at other times it is discontinued, and the two sinuses communicate.—Each sinus commonly opens by a roundish small hole, at the inner and lower part of the internal angular processes, into a sinus formed in the nose, at the upper and back part of the os unguis; near to which there are also some other small sinuses of this bone, the greater part of which open separately nearer the septum narium, and often they terminate in the same common canal with the large ones.

In a natural and sound state, these cavities are of considerable advantage; for the organ of smelling being thus enlarged, the effluvia of odorous bodies more difficultly escape it; and their impressions being more numerous, are therefore stronger, and affect the organ more. These and the other cavities which open into the nose, increase the sound of our voice, and render it more melodious, by serving as so many vaults to resound the notes. Hence people labouring under a coryza, or stoppage of the nose from any other cause, when they are by the vulgar, though falsely, said to speak through their nose, have such a disagreeable harsh voice.—The liquor separated in the membrane of these sinuses, drills down upon the membrane of the nose to keep it moist.

From the description of these sinuses, it is evident, No. 7.