THE SPHENOID BONE. 



73 



etkmoidal spine, for articulation with the cribriform plate of the ethmoid ; behind 

 this a smooth surface presenting, in the median line, a slight longitudinal eminence, 

 with a depression on each side for lodging the olfactory lobes. This surface is 

 bounded behind by a ridge, which forms the anterior border of a narrow, transverse 

 groove, the optic groove, behind which lies the optic commissure ; the ridge terminates 

 on either side of the optic foramen, for the passage of the optic nerve and oph- 

 thalmic artery. Behind the optic groove is a small eminence, olive-like in shape, 

 the olivary process; and still more posteriorly, a deep depression, the pituitary 

 fossa, or sella turcica, which lodges the pituitary body. This fossa is perforated 

 by numerous foramina, for the transmission of nutrient vessels into the substance 

 of the bone. It is bounded in front by two small eminences, one on either side, 

 called the middle clinoid processes (x/r'wy, a bed), which are sometimes connected 

 by a spiculum of bone to the anterior clinoid processes, and behind by a square- 

 shaped plate of bone, the dorsum ephippii or dorsum sellce, 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 fossa, 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 Avith 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 with perpendicular 

 Ethmoidal crest. plate of ethmoid. 



Pterygoid ridge. 



Internal pterygoid plate. 

 Hamular process.' 



FIG. 38. 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. 38) presents, in the middle line, a vertical ridge of bone, the 



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. 



