THE SPHENOID BONE. 



187 



it from the apex of the petrosal. It is here bounded internally by a little tubercle, 

 the petrosal process, at the base of the dorsum, and externally by a very delicate 

 plate, the lingula, which sometimes projects considerably ; these two processes 

 touch either side of the end of the carotid canal in the petrous. The rest of the 

 side of the body is hollowed for the cavernous sinus, in which the carotid artery runs. 

 It is covered below by the origin of the great wing. The posterior surface of the 

 body is rough up to puberty for the cartilage that binds it to the basilar process of 

 the occipital ; later these parts cobssify, and thereafter the posterior surface is made 

 artificially by the saw. The anterior surface presents in the middle a sharp ridge, 

 the sphenoidal crest, ^ to join the vertical plate of the ethmoid. Just at the sides of this 

 the bone is smooth and aids in forming the wall of the nasal fossa. In each lateral 

 half is an opening, the sphenoidal foramen,'^ into the cavity of the bone. The 

 inferior surface presents in the middle a longitudinal swelling, thick behind, 

 narrow and sharp in front, the rostrum, fitting into the vomer and usually joining 

 the lower edge of the crest without interruption. It may stop short of it. On either 

 side of the rostrum there is a smooth triangular surface made of delicate plate, which 

 extends up onto the front, forming the smooth surface beside the crest, and bound- 



FiG. 209. 



Foramen rotundum 



Carotid groove 

 Scaphoid fossa 



Pterygoid fossa 



External pter>'goid plate 



Hamular process 



The sphenoid bone from behind. 



ing a large part of the hole into the antrum. These are the bones of Berlin, or 

 spheyioidal spongy boyies, of which more is to be said under Development (page 191). 



The body of the sphenoid is hollow, enclosing two cavities, the sphenoidal 

 sinuses, separated by a septum, which runs obliquely backward from the crest, so 

 that one sinus is usually much larger than the other. These sinuses have irregular 

 ri(^ges partially subdividing them. They are lined by mucous membrane and open 

 into the nasal cavity by the sphenoidal foramina. The opening is reduced when the 

 ethmoid is in place. 



The great wings ^ have each a cerebral or superior snri2t.ce^ forming a large part 

 of the middle fossa, an external surface looking outward into the temporal and 

 downward into the zygomatic fossa, and an orbital surface forming most of the outer 

 wall of that cavity. The superior surface is smooth and concave ; springing from 

 the side of the basisphenoid, it spreads upward and outward and also backward to 

 fill the gap between the petrous and squamosal parts of the temporal. By the side 

 of the body there is a short canal running forward to open on the front of the bone 

 into the spheno-maxillary fossa ; this is the foramen rotu7idtim for the superior max- 

 illary division of the fifth nerve. A little further back and more internal is a pin- 



* Crista sphenoidnlis. ^ Apertura sinus sphenoidalis. ^ Alae magnae. 



