SPHENOID BONE. 37 



sphenoidal cells. The sphenoidal cells, which are absent in the young 

 subject, are divided by a median septum which is continuous with the 

 crista, and are partially closed by two thin plates of bone (frequently 

 broken away), the sphenoidal spongy bones. On each side of the sphe- 

 noidal cells are the outlets of the optic foramina, sphenoidal fissures, 

 and foramina rotunda, the lesser and greater wings ; and below, the 

 pterygoid processes. Upon the under surface of the body are two 

 thin plates of bone (processus vaginal.es) proceeding from the base of 

 the pterygoid process at each side and intended for articulation with 

 the borders of the vomer. On each of these plates, close to the root of 



Fig. 21.* 



the pterygoid process, is a groove (sometimes a complete canal) con- 

 verted into a canal by the palate bone, the pterygo-palatine canal for 

 the pterygo-palatine artery ; and traversing the roots of the pterygoid 

 processes at their union with the body of the bone are the two ptery- 

 goid or Vidian canals which give passage to the Vidian nerve and 

 artery at each side. 



The posterior surface is flat and rough, and articulates with the 

 basilar process of the occipital bone. In the adult, this union is usually 

 completed by bone ; from which circumstance the sphenoid, in con- 

 junction with the occipital, is described by Soemmering and Meckel 

 as a single bone, under the name of spheno-occipitaL The posterior 



* The antero-inferior view of the sphenoid bone. 1. The ethmoid spine. 

 2. The rostrum. 3. The sphenoidal spongy bone, partly closing the left open- 

 ing of the sphenoidal cells. 4. The lesser wing. 5. The foramen opticum 

 piercing the base of the lesser wing. 6. The sphenoidal fissure. 7. The fora- 

 men rotundum. 8. The orbital surface of the greater wing. 9. Its temporal 

 surface. 10. The pterygoid ridge. 11. The pterygo-palatine canal. 12. The 

 foramen of entrance to the Vidian canal. 13. The internal pterygoid plate. 

 14. The hamular process. 15. The external pterygoid plate. 16 The fora- 

 men spinosum. 17. The foramen ovale. 18. The extremity of the spinous 

 process of the sphenoid. 



