SPHENOID BONE. 



69 



hyoid and stylo-maxillary ; and by the petrous portion, to the levator 

 palati, tensor tympani, and stapedius. 



SPHENOID BONE. The sphenoid (#<p^v, a wedge) is an irregular bone 

 situated at the base of the skull, wedged between the other bones of the 

 cranium, and entering into the formation both of the cranium and face. It 

 bears some resembjance, in form, to a bat with its wings extended, and is 

 divisible into body, wings, and processes. 



The body forms the central mass of the bone, from which the wings and 

 processes are projected. From the upper and anterior part of the body 

 extend on each side two small triangular plates the lesser wings ; from 

 either side and expanding laterally are the greater wings ; proceeding 

 backwards from the base of the greater wings, the spinous processes, and 

 downwards, the pterygoid processes. 



The body presents for examination a superior or cerebral surface, an 

 antero-inferior surface, and a posterior surface. 



Superior Surface. At the anterior extremity of this surface is a small 

 projecting plate, the ethmoidal spine, and spreading out on either side the 

 lesser wings. Behind the ethmoidal spine in the middle line is a rounded 

 elevation, the olivary process, which supports the commissure of the optic 

 nerves ; and on either side of the posterior margin of this process is a 

 tubercle, the middle clinoid process. Passing outwards and forwards from 

 the olivary process, are the optic foramina, which transmit the optic nerves 

 and ophthalmic arteries. Behind the optic foramina are two sharp tuber- 

 cles, the anterior clinoid processes, which are the inner terminations of the 

 lesser wings. Beneath these processes, on the sides of the olivary process, 

 are two depressions* for the last turn of the internal carotid arteries. Be- 

 hind the olivary process is the sella turcica (ephippium), the deep fossa 

 which lodges the pituitary gland and circular sinus ; behind and somewhat 

 overhanging the sella turcica, is a broad rough plate (dorsum ephippii) 

 bounded at each angle by a tubercle, the posterior clinoid, processes ; and 

 behind this plate an inclining surface (clivus Blumenbachii), which is con- 

 tinuous with the basilar process of the occipital bone. On either side of 

 the sella turcica is a broad 



groove (carotid) which- lodges Flg - 3L t 



the internal carotid artery, the 

 cavernous sinus, and the orbi- 

 tal nerves. Immediately exter- 

 nal to this groove, at the junc- 

 tion of the greater wings with 

 the body, are four foramina : 

 the first is a broad interval, 

 the sphenoidal fissure, which 

 separates the greater and lesser 

 wings, and transmits the third, 



* These depressions are occasionally, as in a skull before me, converted into fora 

 mina by the extension of a short bony pillar from the middle to the anterior clinoid 

 process. 



f The superior or cerebral surface of the sphenoid bone. 1. The processus olivaris. 

 2. The ethmoidal spine. 3. The lesser wing of the left side. 4. The cerebral surface 

 of the greater wing of the same side. 5. The spinous process. 6. The extremfty of 

 the pterygoid process of the same side, projecting downwards from the ur.der surfaoe 

 of the body of the bone. 7 The foramen opticum. 8. The anterior clynoid process. 





