The Compleat Surgeon / or, the whole Art of Surgery explain'd in a most familiar Method.

by M. Le Clerc

In the Portion of the Os Sphenoides, that makes the Basis of the Orbit, lies a Fissure about seven or eight Hairs breadth long, which is to be observ'd chiefly at the bottom, that is to say, below the Hole, thro' which the Optick Nerve passeth; where it is almost round, and larger than at the top, where it is terminated in a very long and acute Angle.

There are many Pairs of Nerves that enter into the Orbit thro' this Fissure, viz. 1. The third Pair, call'd the Motorii Oculorum. 2. The fourth Pair, nam'd Pathetici, by Dr. Willis. And 3. The whole sixth Pair. Besides these three Pairs, which go entire thro' this Cleft, there is also a Passage for the upper Branch of the foremost Fibre of the fifth Pair, which the same renowned Physician calls the Ophthalmick Branch. Beyond the lower-part of the said Fissure, toward the hinder-part of the Head, is to be seen

in the Os Sphenoides on each side, a Hole that doth not penetrate the Basis of the Skull, but makes a kind of Ductus, about an Hair's breadth long, which is open'd behind the Orbit on the top of the Space between the Apophysis Pterygoides, and the third Bone of the Jaw; thro' this Ductus runs the lower Branch of the foremost Fibre of the fifth Pair.

About the length of two Hairs breadth beyond these Ductus's, we may also discover in the Os Sphenoides, or Wedge-like Bone, two Holes of an Oblong and almost Oval Figure, which are plac'd in the hindermost sides of that of the Os Sphenoides, and gives passage to the hindermost Fibre of the fifth Pair.

The Hole thro' which runs the Auditory Nerve, that makes the seventh Pair, is in the middle of the hinder-part of the Os Petrosum, that looks toward the Cerebellum: This Hole being very large, is the Entrance of a Ductus that is hollow'd in the Os Petrosum, and which sinking obliquely from the fore-part backward, for the depth of about two Hairs breadth, forms as it were the bottom of a Sack, the lowermost part whereof is terminated partly by the Basis of the Cochlea, and partly by a Portion of the Mouth of the Vestibulum. At the bottom of this Ductus are many Holes, but the most considerable is that of the upper-part, thro' which passeth a Portion of the Auditory Nerve. This is also the Entrance of another Ductus made in the Os Petrosum, which is open'd between the Apophysis Mastoides and Styloides: These other Holes afford a Passage to the Branches of the soft Portion of the same Auditory Nerve.

Below this Ductus there is a remarkable Hole form'd by the meeting of two hollow Cuts the larger whereof is in the Occipital Bone and the other in the lower-part of the Apophysis Petrosi: From the middle of the upper-part of this Hole issueth forth a small Prominence or bony Point, whereto is join'd an Appendix of the Dura Mater, which divides the Hole into two parts; so that thro' the foremost Orifice passeth the Nerve of the eighth Pair, and that which is call'd the Spinal Nerve. We shall have occasion hereafter to shew the Use of the hinder Orifice.

Near the great Hole of the Occipital Bone from whence proceeds the Medulla Oblongata, we may observe a Hole almost round and oblong thro' which passeth the Nerve of the ninth Pair. This Hole is entirely situated in the Occipital Bone, and making a little Way in the Bone passeth obliquely from the back-part forward. In the inside of the Skull this Hole is sometimes double, but its two Entrances are re-united in the outward-part of the Skull; and the two Branches that form the Origine of this Nerve and which pass thro' these two Holes, are likewise re-united at their Departure, These are the Passages of the nine Pairs of Nerves that proceed from the Medulla Oblongata, and it remains only to show that Paths thro' which the Intercostal Nerve goes forth, as also that of the tenth Pair. The Intercostal runs out of the Skull thro' the Ductus that gives Entrance to the Internal Carotick Artery. As for the tenth Pair, in regard that it ariseth from the Marrow which is enclos'd between the Occipital

Bone and the first Vertebra, it goes forth thro' the Hole of the Dura Mater, where the Vertebral Artery enters.

To know well the Holes thro' which the Vessels that belong to the inner-part of the Head enter, and issue forth, it is requisite to distinguish them into those which are distributed to the Dura Mater, and those that are appointed for the Brain. The Vessels of the Dura Mater, are Branches of the Carotick or Vertebral Arteries.