150 



THE SKELETON. 



presenting, in the median line, a slight longitudinal eminence, with a depression 

 on each side, for lodging the olfactory nerves. A narrow transverse groove, 

 the optic groove, bounds the above-mentioned surface behind ; it lodges the 

 optic commissure, and terminates on either side in the optic foramen, for the 

 passage of the optic nerve and ophthalmic artery. Behind the optic groove is a 

 small eminence, olive-like in shape, the olivary process ; and still more poste- 

 riorly, 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 to the substance of the bone. It is bounded 

 in front by two small eminences, one on either side, called the middle clinoid 

 processes (xuw?, a bed), and behind by a square-shaped plate of bone, terminat- 

 ing at each superior angle in a tubercle, the posterior clinoid processes, the 

 size and form of which vary considerably in different individuals. These pro- 

 cesses deepen the pituitary fossa, and serve for the attachment of prolongations 

 from the tentorium cerebelli. The sides of the plate of bone supporting the 

 posterior clinoid processes are notched for the passage of the sixth pair of 

 nerves; and behind, this plate of bone presents a shallow depression, which 

 slopes obliquely backwards, and is continuous with the basilar groove of the 

 occipital bone; it supports 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 cavernous groove. The 

 posterior surface, quadrilateral in form, articulates with 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. 102) pre- 



Fig. 102. Sphenoid Bone. Anterior Surface. 1 



LAXATOR TYMPANI 



sents, in the middle line, a vertical lamella of bone 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 the irregular openings leading into the sphenoid 

 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 



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. 



