The grcat wing or alisphenoid supports the anterior pole of the temporo-sphenoida! lobe of tlw<cerebrum, is therefore concave on its upper surface in all directions, forming the front part of the middle fossa on each side, and exhibits impressions for the cerebral gyri. The wing is thickened in front and externally, so that, in addition to its upper and lower surfaces, it presents an anterior or orbital and an outer or temporal aspect.
The upper concave cerebral aspect is in a very general way triangular, attached to the body by the internal angle : the front border, raised, is separated from the small wing by the sphenoidal fissure and, outside this, articulates with the frontal: the outer and upper angle, raised, is blunt and articulates with the parietal: the outer or posteroexternal border descends rapidly from this angle in a concave line that articulates with the temporal squama and runs downwards, backwards, and inwards : the posterior angle projects well back beyond the level of the rest of the bone and fits in between the squamous and petrous temporal: the inner or postero-internal border, articulating with the petrous, runs from this angle towards the body, where it is joined by the lingula and marked by the carotid groove. This surface presents (Fig. 179) :-
(a) Foramen spinosum, in posterior angle, for meningeal vessels and recurrent branch of mandibular nerve ; from this a grooye for the anterior division of the artery is usually found running along the postero-external border, but this is occasionally on the temporal s de of the suture. A small canalis innominatus is occasionally seen internal to the foramen spinosum, for the passage of the small superficial petrosal nerve.
(b) Foramen ovale, for the mandibular division of the fifth nerve, its motor root, and the small meningeal artery.
(c) Foramen rotundum, for the superior maxillary division of the nerve. Notice that this opening is just below the inner end of the sphenoidal fissure, and it may be looked on as part of this fissure cut off by extending ossification.
Articulate the bone with the temporal and observe the position of the Gasserian ganglion (Fig. 181). It lies on the petrous and over the outer part of the foramen lacerum, just behind and internal to the foramen ovale, into which its largest offset goes.
The other two divisions of the nerve, running to the foramen rotundum and sphenoidal fissure respectively, are therefore internal to and above the mandibular division and are in relation with the outer wall of the cavernous sinus.
The bone is covered on this aspect by dura mater, and the nerves and artery lie between it and the membrane, which extends from the front border of the wing on to the lesser wing and thus covers in the sphenoidal fissure.
The lower or basal aspect of the wing is small, and corresponds with the inner part of the wing and with that portion that extends back to form the posterior angle : the outer part of the wing is turned up, forming a continuous curve with the remainder on the cerebral aspect, but being marked off from the lower surface externally by a definite border or ridge, the inferior temporal crest. The basal surface can thus be said to lie between this crest and the external pterygoid plate, while the temporal surface lies above the crest.
The basal surface gives origin to External Pterygoid from the whole of the surface outside the pterygoid plate, the area of origin being bounded in front by the pterygoid ridge, which turns outwards from the front of the plate and usually shows a pterygoid spine to which some aponeurotic fibres on the superficial surface of the muscle are attached. But behind the level of the external plate, where the bony surface does not give origin to the muscle but is in contact with it, the wing is seen to narrow sharply to the posterior angle, where it bears the spine, to which the long internal lateral ligament of the mandible is fastened. Along the postero-internal edge the Tensor palati arises, and immediately external to this are the leuer openings of the oval and spinous foramina.
Examine this region on the skull. The basal aspect of the bone is continuous with that of the eminentia articularis on the temporal squamous, and the inferior temporal crest is continued back on the temporal to run into the front border of the anterior zygomatic root : evidently all this basal area is in relation with the External Pterygoid as this passes to its insertion into the neck and capsule of the lower jaw, and the muscle covers the bone as far out as the lower temporal ridge : hence the Temporal muscle, coming down over the ridge, makes the immediate outer relation of the External Pterygoid (Fig. 182).
Now follow the course of the nerves that run directly out from the mandibular nerve : they must lie between the bone and the Pterygoid muscle. The arrangement of the deep temporal filaments is very variable, but a typical one would have a middle deep temporal running by itself outward and a little forwards from the foramen ovale ; a line showing its course would cross the basal aspect of the great wing and would just lie on the temporal bone as it reached the temporal ridge, turning round this to run up on the deep surface of the Temporal muscle. The bone is sometime; grooved by the nerve near the ridge. The masseteric nerve runs behind the other and more directly outward, thus passing on to the front part of the eminentia articularis after a shorter course on the sphenoid : on the eminence it runs out to the back of the Masseter, passing behind the Temporal tendon and giving a posterior deep temporal filament up along the tendon (Fig. 182).
The structures passing through the foramina are evidently placed between the Tensor palati and the External Pterygoid.