THE SPHENOID BOXE. 



181 



shaped plate of bone, the dor sum epliippii or dorsum sella\ terminating at each 

 superior angle in a tubercle, the posterior clinoid processes, the size and form of 

 which vary considerably in different individuals. These processes deepen the 

 pituitary fo><a. and serve for the attachment of prolongations from the tentorium 

 cerebelli. The sides of the dorsum ephippii are notched for the passage of the 

 sixth pair of nerves, and below present a sharp process, the petrosal process, which 

 is joined to the apex of the petrous portion of the temporal bone, forming the inner 

 boundary of the middle lacerated foramen. Behind this plate the bone presents 

 a shallow depression, which slopes obliquely backward, and is continuous with the 

 basilar groove of the occipital bone : it is called the clivus. and supports the upper 

 part of the pons Varolii. On either side of the body is a broad groove, curved 

 something like the italic letter /; it lodges the internal carotid artery and the 

 cavernous sinus, and is called the carotid or cavernous groove. Along the outer 

 margin of this groove, at its posterior part, is a ridge of bone in the angle between 

 the body and greater wing, called the lingula. The posterior surface, quadrilateral 



Articulates irith perpendicular 

 Ethmoidal crest. plate of ethmoi< 



Pterygoid ridge 



Internal pterygoid pla 

 Hamidar process. 



FIG. 144. Sphenoid bone. Anterior surface. 1 



in form, is joined to the basilar process of the occipital bone. During childhood 

 these bones are separated by a layer of cartilage ; but in after-life (between the 

 eighteenth and twenty-fifth years) this becomes ossified, ossification commencing 

 above and extending downward : and the two bones then form one piece. The 

 anterior surface (Fig. 144) presents, in the middle line, a vertical ridge of bone, the 

 etlimoi-lal crest, which articulates in front with the perpendicular plate of the 

 ethmoid, forming part of the septum of the nose. On either side of it are irregular 

 openings leading into the sphenoidal cells or sinuses. These are two large irregular 

 cavities hollowed out of the interior of the body of the sphenoid bone, and separated 

 from one another by a more or less complete perpendicular bony septum. Their 

 form and size vary considerably: they are seldom symmetrical, and are often 

 partially subdivided 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 nor 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 occasionally 



1 In this figure, both the anterior and inferior surfaces of the body of the sphenoid bone are 

 shown, the bone being held with the pterygoid processes almost horizontal. 



