THE SPHENOID BONE 49 



the inferior boundary of the sphenoidal fissure, and often 

 shows a bony projection for the lower head of the external 

 rectus. 



The ptcrygoid (wing-like) processes project downward and 

 forward (angle of 110 to 115 degrees) from the junction of the 

 body and great wings. Some consider them to rise from two 

 roots, one representing a transverse process, one a rib, and 

 the Vidian canal, the costotransverse foramen. Each consists 

 of two plates united in front and diverging behind, forming 

 the pterygoid fossa for the origin of the internal pterygoid 

 muscle. The external plate is broad and extends out and 

 back, and gives origin by its outer surface to the external 

 pterygoid muscle. The internal plate is long and narrow, and 

 prolonged below into the hamular process (hook-like), around 

 which plays the tendon of the tensor palati, muscle. The 

 upper part of the inner plate turns in beneath the body, and 

 remains distinct as a slightly raised edge, the vaginal process, 

 which meets the everted margin of the vomer. At the angle 

 of the vaginal process with the internal plate is a groove which, 

 with the sphenoidal process of the palate, forms the ptcry go- 

 palatine canal. Posteriorly, at the base of the inner plate, 

 is the pterygoid tubercle, to the inner side of and below the 

 Vidian canal; between this and the pterygoid fossa is the 

 scaphoid fossa for the origin of the tensor palati muscle. Lower 

 down, on the posterior margin of the plate, is the processus 

 tubarius, which supports the cartilage of the Eustachian tube. 

 Between the lower ends of the plates is the ptcrygoid notch, 

 occupied by the pyramidal process of the palate bone. 



Fissures and Foramina of the Sphenoid. Each half pre- 

 sents a fissure, four foramina, and a canal. The sphenoidal 

 fissure is the oblique interval between the great and small 

 wings, closed externally by the frontal bone. It opens into 

 the orbit and transmits the third, fourth, ophthalmic division 

 of the fifth, and the sixth cranial nerves, some sympathetic 

 filaments from the cavernous plexus, the orbital branch of 

 the middle meningeal artery, recurrent branch of the lacrymal 

 artery, and the ophthalmic vein. Above and to the inside 

 of this fissure is the optic foramen, piercing the base of the 

 small wing and transmitting the optic nerve and ophthalmic 

 artery. The foramen, rotundum pierces the great wing below 

 the sphenoidal fissure and transmits the superior maxillary 

 4 



