The pterygoid processes consist of two plates, with a triancfular separation inferi orly, and they are ca°11ed the external and the internal pterygoid processes or plates. The external is broader, thinner, and is directed more outwardly than the internal ; its outer surface, which also looks a little forwards, gives attachment to the external pterygoid, its inner to the internal pterygoid muscles. The internal is nearly vertical ; it is pierced longi tudinally at its base by the canalis Vidianus for the passage of the vessel and nerve which bear that name ; at its inferior extremity there is a hook (the hamular process ), which acts as a pulley for the tensor palati muscle, the attachment of which to the outer side of the internal pterygoid process is shewn by a sul cus which is most evident at the base (fossa navicularis) ; to its anterior edge is applied a thin plate of the palatine bone, thus sepa rating it from the superior maxillary, and to its posterior edge is affixed the aponeurotic origin of the superior constrictor of the pha rynx. The concavity between the two pro cesses is the jbssa pterygoidea which is occu pied by the internal pterygoid muscle, and the notch at the lower part (the hiatus pala tinus) is filled up by the pterygoid process of the palatine bone.
The external mi.-face of each ala is continu ous with the inferior; it is concave from before to behind, and convex from above downwards; it contributes to the formation of the temporal fossa, and the continuation of the sulcus tem poralis is evident at its anterior part (S, fig. 373).
The anterior surface forms the major part of the external wall of the orbit, is oblong, di rected forwards and inwards, and is narrower at its extremities than in its middle.
The superior border of the great wing sepa rates the orbital from the cerebral surface ; it presents a sharp smooth edge on its inner half, and a rough irregular surface on its outer half; it is convex, and its convexity is directed up wards, forwards, and ini,vards. The sharp internal half concurs with the aim minores to form the sphenoidal fissure, which vvill be de scribed with those processes. The external rough half becomes broader as it passes out wards, so as to produce a triangular indented surface, the outer edge of which is prolonged at the expense of the inner table in such a manner that it overlaps the frontal bone which is affixed on ,it, and this prolongation is con tinued without the indented surface, so as to grasp the anterior inferior ,spinous process of the parietal bone.
The external border is nearly the reverse of the former. It is concave, and looks outwards and backwards, and it is articulated in its entire extent to the squamous portion of the temporal bone, by which it is overlapped in its anterior third, and receiving and supporting it in its two posterior thirds the former at the expense of its outer table, t'he latter at that of the in ternal.
The posterior border is applied against the outer side of the petrous portion of the tem poral bone, and extends from the body of the sphenoid to the posterior extremity of ,the ex ternal border. The junction of these two bor ders forms the spinous process, which is received into the angle of the petrous and squamous portions of the temporal bone. The laxator tympani muscle arises from this process, and the styloid process before described descends from it. The angle which exists where this border departs from the body, in part forms the foramen lacerum anterius, an opening which, in the recent skull, is closed by cartilage.
The anterior border consists of two portions which join with each other at an angle. Of these the upper is indented, separates the or bital from the temporal surface, and articulates with the malar bone. The inferior portion is smooth, and forms with the palatine and supe rior maxillary bone, the fissura lacera orbitalis iVerior.
The alee minores are on the upper and an terior part of the body of the bone ; they ex tend outwards over the superior borders of the greater wings, and, gradually tapering, they at last end in a point.
The upper surface of each ala minor is smooth, and partly forms the anterior fossw of the skull. The processus ethmoidalis is a thin lamina somewhat triangular in form, prolonged for vvards on the median line to articulate with the cribriform plate of the ethmoid bone. Passing backwards from this process, there is a slightly elevated line separating the depressions which on each side receive the olfactory nerves, and terminated posteriorly by a tubercle (processus olivaris) marking the decussation of the optic nerves, and having upon it a transverse depression for the lodgement of their com missure. This depression terminates on each side in the foramen opticum for the passage of the optic nerve and the ophthalmic artery, in such a manner that the lesser ala appears to arise by two roots, one above and the other below the foramen. From the sides of the processus ethmoidalis there pass the two transverse spi nous processes, being the anterior serrated mar gins of the wings ; they are articulated to the orbitar processes of the frontal bones, and sometimes join by their extremities the great wings; thereby, in such a case, converting the superior orbital fissure into a foramen without the aid of the frontal bone. The posterior margins of the aim minores are smooth and less sharp than the anterior ; they are pro longed backwards and inwards, so as to form on each side a short and thick triangular pro cess, the apex being directed backwards, called the anterior ephippial (anterior clinoid) pro cess, to which the cornua of the lunated margin of the tentorium are attached.