SPHENOID BONE. 151 



by irregular osseous laminae. Occasionally they extend into the basilar process 

 of the occipital nearly as far as the foramen magnum. The septum is seldom 

 quite vertical, being commonly bent to one or the other side. These sinuses 

 do not exist in children, but they increase in size as age advances. They are 

 partially closed, in front and below, by two thin curved plates of bone; the 

 sphenoidal turbinated bones, leaving a round opening at their upper parts, by 

 which they communicate with the upper and back part of the nose, and occa- 

 sionally with the posterior ethmoidal cells or sinuses. The lateral margins of 

 this surface present a serrated edge, which articulates with the os planum of the 

 ethmoid, completing the posterior ethmoidal cells; the lower margin, also rough 

 and serrated, articulates with the orbital process of the palate bone ; and the 

 upper margin with the orbital plate of the frontal bone. The inferior surface 

 presents, in the middle line, a triangular spine, the rostrum, which is continuous 

 with the vertical plate on the anterior surface, and is received into a deep fissure 

 between the alas of the vomer. On each side may be seen a projecting lamina 

 of bone, which runs horizontally inwards from near the base of the pterygoid 

 process : these plates, termed the vaginal processes, articulate with the edges 

 of the vomer. Close to the root of the pterygoid process is a groove, formed 

 into a complete canal when articulated with the sphenoidal process of the palate 

 bone; it is called the pterygo-palatine canal, and transmits the pterygo-palatine 

 vessels and pharyngeal nerve. 



The Greater Wings are two strong processes of bone, which arise from the 

 sides of the body, and are curved in a direction upwards, outwards, and back- 

 wards ; being prolonged behind into a sharp-pointed extremity, the spinous 

 process of the sphenoid. Each wing presents three surfaces arid a circumfer- 

 ence* The superior or cerebral surface (Fig. 101) forms part of the middle fossa 

 of the skull ; it is deeply concave, and presents eminences and depressions for 

 the convolutions of the brain. At its anterior and internal part is seen a cir- 

 cular aperture, the foramen rotundurn, for the transmission of the second divi- 

 sion of the fifth nerve. Behind and external to this is a large oval foramen, 

 the foramen ovale, for the transmission of the third division of the fifth nerve, 

 the small meningeal artery, and the small petrosal nerve. At the inner side 

 of the foramen ovale, a small aperture may occasionally be seen opposite the 

 root of the pterygoid process; it is the foramen Vesalii, -transmitting a small 

 vein. Lastly, in the apex of the spine of the sphenoid is a short canal, some- 

 times double, the foramen spinosum; it transmits the middle meningeal artery. 

 The external surface (Fig. 102) is convex, and divided by a transverse ridge, 

 the pterygoid ridge, into two portions. The superior or larger, convex from 

 above downwards, concave from before backwards, enters into the formation 

 of the temporal fossa, and attaches part of the temporal muscle. The inferior 

 portion, smaller in size and concave, enters into the formation of the zygomatic 

 fossa, and affords attachment to the External Pterygoid muscle. It presents, 

 at its posterior part, a sharp-pointed eminence of bone, the spinous process, to 

 which is connected the internal lateral ligament of the lower jaw, and the 

 Laxator Tympani muscle. The pterygoid ridge, dividing the temporal and 

 zygomatic portions, gives attachment to part of the External Pterygoid muscle. 

 At its inner extremity is a triangular spine of bone, which serves to increase 

 the extent of origin of this muscle. The anterior or orbital surface, smooth and 

 quadrilateral in form, assists in forming the outer wall of the orbit. It is 

 bounded above by a serrated edge, for articulation with the frontal bone ; 

 below, by a rounded border, which enters into the formation of the spheno- 

 maxillary fissure ; internally, it enters into the formation of the sphenoidal 

 fissure ; whilst externally it presents a serrated margin, for articulation with 

 the malar bone. At the upper part of the inner border is a notch for the trans- 

 mission of a branch of the ophthalmic artery; and at its lower part a small 

 pointed spine of bone, which serves for the attachment of part of the lower 

 head of the External Eectus. One or two small foramina may occasionally be 



