SPHENOID BOXE. 



41 



separated from it oy a thin lamella, the 2^^'ocessiis cochleariformis, is a 

 small passage which lodges the tensor tympani muscle. The imaterior 

 harder articulates with the basilar process of the occipital bone, and 

 bounds the foramen lacerum posterius. 



Sraall Foramina. — The opening of the a/pu'ductus re.stlhuU is a naiTOW fissure, 

 covered by a depressed scale of bone, and situated on the posterior siui'ace of the 

 petrous bone, about three lines behind the internal auditory meatus ; that of the 

 n/jtirdi/ctH.'i cochlea' is a small foramen, beginning in a three-sided wider depression 

 in the pos-terior margin, directly below the internal auditory meatus. In the plate 

 between the jugular fossa and the carotid canal is the foramen by which the 

 nerve of Jacobson passes to the tpnpaniim. In the ascending part of the carotid 

 canal is the minute foramen for the tympanic branch of the carotid plexus. In 

 the jugular fossa are a gi'oove ancl foramen for the aiiricular branch of the vagus 

 nei-ve ; and parallel to the hiatus Fallopii, close to the canal for the tensor 

 tympani muscle, are a groove and foramen for the small superficial petrosal 

 nei-ve. 



The description of the small Ijones of the ear with the tjTnpanum and internal 

 ear. will be found in the chapter on the Organs of the Senses. 



THE SPHENOID BONE. 



Tlie sphenoid, or wedge-shaped bone, is placed across the base of the 

 skull, near its middle. It enters into the formation of the cavity of the 

 cranium, the orbits, and the posterior nares. It is of very irregular 

 shape, and consists of a central part or hodtj, a pair of lateral expan- 



Fis. 36. 



Fig. 36. — The Sphenoid Bone from above and behind. (A. T.) f 



1, the basilar surface, sawn separate from the occipital bone ; 2, Dorsum sellre, or 

 inclined surface of the body terminating superiorly in the two posterior clinoid processes ; 

 3, is i^laced on the olivary eminence or process, and between it and 2 is the sella turcica, 

 or pituitaiy fossa ; in front of 3 is the transverse gi-oove of the optic commissure ; 4, the 

 side of the body with the sigmoid groove of the internal carotid artery and cavernous 

 sinus ; 5, the lesser wing ; x, the anterior clinoid jn-ocess ; 6, the ethmoid spine ; 7, 

 the cerebral surface of tiie greater wing ; 8, the upper angle of the greater wing, which 

 articulates with the parietal bone ; 9, the spinous process ; 10, the external, and 11, the 

 intei-nal pterygoid process ; 11, is jilaced opposite the hamular i^rocess and groove for the 

 tendon of the tensor palati muscle ; 12, the optic foramen, 13, the sphenoidal fissure or 

 foramen lacerum orbitale ; 14, the foramen rotundum ; 15, the foramen ovale ; 16, the 

 foramen spinosum ; 17, is placed above the posterior opening of the pterygoid or Vidian 

 foramen. 



