1 86 



HUMAN ANATOMY. 



THE SPHENOID BONE. 

 In the adult this bone ' consists of a cubical body, from the sides of which arise 

 the great wi7igs, from its front the lesser wings, and from below the pterygoid pro- 

 cesses. Both development and copiparative anatomy show that these parts represent 

 several bones. The body consists of two parts, a posterior and an anterior. The 

 posterior, the basisphenoid, is the centre of the middle fossa of the base of the skuU ; 

 from its sides spread the great wings, or alisphenoids .. These with the temporal 

 bones complete the middle fossa. The anterior part, the prespherioid, inseparably 

 connected with the basisphenoid, is in both the middle and the anterior fossae. The 

 lesser wings, the orbito- sphenoids, spread out from the presphenoid and cover the 

 apices of the orbits. 'Wv^ pterygoid processes consist each of two plates, the inner of 

 which represents a separate bone of the face, the outer being an expansion from the 

 alisphenoid. Two bones called the coriiua sphe?ioidalia, or sphe7ioidal tiifbifiates, of 

 independent origin, ultimately form a part of the body of the sphenoid. 



Optic foramen 



Fig. 208. 



Sphenoidal turbinate 



• Sphenoidal foramen 



vj'\t^g 



Foramen ro- 

 tundum 



Infratemporal 

 crest 



Zygomatic 

 surface 



External ptery 

 goid plate 



Hamular process 



Pterygoid notch 



Internal pterygoid plate 

 The sphenoid bone from before. 



The Body. — It is necessary to describe the basisphenoid and the presphenoid 

 together, since they form the roughly cubical body. The superior surface con- 

 tains the d&Q^ pituitary fossa,'^ or sella turcica, in which hangs the pituitary body 

 from the brain. Behind it is the dorsum sellce, a raised plate continuous with the 

 surface of the basilar process of the occipital and which completes the posterior fossa. 

 Its outer angles are knobs pointing both forward and backward, the posterior clinoid 

 processed, to which the tentorium is fastened. Beneath these, on either side of the 

 dorsum, is a groove for the sixth nerve. In front of the sella is the olivary eminence^ 

 (of the presphenoid), which is usually an oval swelling, though it may be plane or 

 concave. At its sides grooves, often very poorly marked, lead to the optic foraniiiia. 

 The posterior edge of this eminence is sometimes grooved fo| a vein and sometimes 

 sharp. Its lateral ends may become tubercles, the middle clinoid processes. The 

 olivary eminence is in most cases bounded in front by a transverse elevation con- 

 necting the lesser wings, of which, indeed, it is a part, forming, when present, the 

 separation of the anterior and middle fossae. The front border presents in the 

 median line a triangular point, the ethmoidal spine. 



At each lateral surface of the body is the carotid gf'oove^ for the internal 

 carotid artery. It is well marked only at the posterior edge, where the artery enters 



^ Os sphenoidale. '-^ Fossa hypo|»ljysBOS. ^Tuberculum sellae. * Sulcus caroticus. 



