THE SPHENOID BONE 51 



joined to the basilar part of the occipital; at the line of junction there is 

 dorsally a transverse elevation, the spheno-occipital crest (Crista spheno- 

 occipitalis). 



The orbital wings (Alte orbitales) curve upward and soinewliat outward from 

 the sides of the body of the pre-sphenoid. Their inner or cerebral surfaces are 

 concave, and are marked b>' digital impressions (Impressiones digitate) for the gyri 

 of the cerebrum. The external surface is convex and is largely concealed by the 

 overlapping temporal wing and the squamous temporal and frontal bones; a 

 narrow part of it (Facies orbitalis) is uncovered on the innei- wail of the orbital 

 cavity at the sphenoidal notch of the frontal bone. The dorsal border unites with 

 the frontal bone at the spheno-frontal suture. The anterior border joins the eth- 

 moid at the spheno-cthmoidal suture; at its lower part it concurs with the frontal in 

 the formation of the ethmoidal (or internal orbital) foramen. The posterior border 

 is overlapped by the temporal wing and the sc^uamous temporal. The root of the 

 wing is perforated by the optic foramen. Immediately below and behind the latter 

 (i. e., beneath the root) is the foramen lacerum orbitale or orbital fissure. Below 

 this, and separated from it usually by a thin plate, is a larger opening, the foramen 

 rotundum, which is bounded externally by the root of the pterygoid process. Be- 

 hind these foramina is the pterygoid crest (Crista pterygoidea), which is continued 

 downward and forward on the pterygoid process; on its upper part may be found 

 the small and inconstant trochlear (or pathetic) foramen. Just behind the crest 

 is the temporal foramen (For. alare parvum), through which the anterior deep 

 temporal artery emerges from the alar canal of the pterygoid process. 



The temporal wings (Alae temporales) extend outward and somewhat upward 

 from the body of the post-sphenoid; they are irregularly quadrilateral in outline. 

 The external surface (Facies temporalis) enters into the formation of the infra- 

 temporal fossa, and bears the pterygoid process on its anterior part; at the junction 

 with the body there is a small groove for the pterygoid nerve. The internal 

 surface (Facies cerebralis) presents, at the junction with the body, two longitudinal 

 grooves (Sulci nervorum).' The outer groove is the larger, and leads forward to 

 the foramen rotundum; it contains the maxillary nerve. The inner groove con- 

 ducts to the orbital fissure, and contains the third, sixth, and ophthalmic nerves. 

 The outer groove is bounded externally by a thin overhanging crest, on which is a 

 small groove for the fourth nerve. The remainder of the surface is concave and 

 supports the pyriform lobe of the brain. The dorsal border joins the squamous 

 temporal at the spheno-squamous suture. The anterior border joins the orbital 

 wing. The posterior border forms the anterior boundary of the foramen lacerum; 

 it presents three notches, which are (from within outward) the carotid, oval, and 

 spinous (Incisura carotica, ovaUs, spinosa). The angle of junction of the dorsal 

 and posterior borders articulates with the parietal bone. 



The pterygoid processes (Processus pterygoidei) arise from the temporal wings 

 and the body. They project downward and forward, and curve outward at the 

 lower part. The root is perforated by the alar canal (Canalis alaris),^ which 

 transmits the internal maxillary artery. From this canal a branch leads upward 

 and forward to open at the temporal foramen. The external surface is concave, and 

 is marked by lines for muscular attachment. The internal surface is largely con- 

 cealed by the overlapping palate and pterygoid bones, with which it concurs in the 

 formation of the pterygoid or Vidian canal. 



Development. — The sphenoid is ossified in cartilage, and consists in early life 

 of two distinct parts, the pre-sphenoid and post-sphenoid. The former develops 

 from two centers, one in each wing; the latter has three centers, one for the body 

 and one for each wing. The pterygoid processes ossify from the centers of the 

 temporal wings. 



1 This is also called the subsphenoidal canal or pterygoid foramen. 



