Fig. 371.
occipital (0, fig. 372) is behind it, the two temporal (T, fig. 370) are on its sides, and the two parietal (P, fig. 370) are above it.
The sphenoid bone (from oply, cuneus, os sphenoidale ; Germ. Sphenoidal-knochen, Keil knochen) comprehends the quadrilateral mass which forms the centre of the frame-work, the anterior ribs which support the frontal and partly the lateral domes, and the depending pillars -which form the boundaries of the face ; it extends to each temple, is behind and in part forms the orbits and the nose, and is also behind but in close connexion with the bones of the face.
The central portion is called the body, and the diverging processes are named aim majores and aloe minores.
The body is of a quadrilateral figure, hollow and divided by a partition into two chambers (the Thenoidal cells, s, fig. 371), which open The anterior surface exhibits the openings of the sphenoidal cells, having, between them, and apparently a continuation of their septum, a prominent ridge which articulates with the ver tical plate of the ethmoid, and, below them, the triangular curved processes denominated the turbinated proceises of the sphenoid bone. Ex ternally to these foramina and turbinated pro cesses on each side is a rough line for the arti culation, in its two superior thirds, of the orbital plate of the ethmoid, and, in its inferior third, of the orbitar process of the palatine bone. To the outer side of this rough line is a smooth surface which contributes to the formation of the orbit.
The posterior surface is rough, quadrilateral, and at an early age becomes indissolubly united to the basilar process of the occipital bone (d, fig. 371) for which reason Scemmerring and Meckel have regarded as one, the occi pital and sphenoid bones, and as such have described it under the name of os basilare.
This surface is bounded superiorly by the basilar process before mentioned, which is placed with such a degree of obliquity, that it may be questioned whether it be on the posterior or superior surface of the body of the bone. It is smooth, slightly concave, and on its edges may often be seen the commencement of the sulci basilares for the lodgement of the basilar sinuses.
The alex Majores are those large curved pro cesses, which, stretching outwards forwards, and upwards, contribute to form ;be middle fossw of the skull, the orbits, and the temples.
The upper surfice of each ala, that which in part forms the middle fossa of the base of the skull, is concave from side to side, and still more so from behind forwards. On it are seen (though not so distinctly) the digital impres sions which mark the lodgement of convo lutions of the brain on the cerebral surface of the other bones of the skull. Close to the spot where it departs from the body of the bone there is a sulcus directed forwards, and ter minating in a round hole (fbramen rotundum ) for the exit of the superior maxillary branch of the par trigeminum or fifth pair of nerves. More outwardly, and behind the plane of the posterior edge of the body of the bone, is a large oval opening (foramen ovale), di rected downwards and slightly outwards for the transmission of the inferior maxillary branch of the par trigeminum and the entrance of the ascending pharyngeal artery, which then be comes a menincreal vessel. Behind this fora men is another (theforamen spinale), which is very small, and affords entrance to the middle meningeal artery.
On the inferior surface are seen the pterygoid processes descending from the great wing where it joins the body of the bone, to afford a resist ing surface against which the bones of the face may be grouped. Anterior to these processes is the termination of theforamen rotundum, the opening of which is directed somewhat out wards, and from which there passes, outwards and upwards, a groove ( sulcus temporalis) for a deep temporal branch of the superior maxil lary nerve. Behind the pterygoid processes, and extending from the base of the internal to the extremity of the wing, is the sulcus Eusta chianus, which lodges part of the Eustachian tube, and on the outer side of this sulcus are seen successively the foramen ovale and the foramen spinale. Immediately behind the lat ter opening, and overhanging the Eustachian tube, is the styloid process, to which the inter nal lateral ligament of the lower jaw is attached. On the outer side of the pterygoid processes is a plain surface forming part of the zygomatic fossa, and bounded externally by a crest, which marks the division between the zygomatic and the temporal fossm, and which intervenes be tween the superior attachment of the external pterygoid and the inferior attachment of the temporal muscles.