SPHENOID BONE. 35 



Attachment of Muscles. To fourteen ; by the squamous portion, 

 to the temporal ; by the zygoma, to the masseter ; by the mastoid por- 

 tion, to the occipito-frontalis, splenius capitis, sterno-mastoid, trachelo- 

 mastoid, digastricus and retrahens aurem ; by the styloid process, to 

 the stylo- pharyngeus, stylo-hyoideus, stylo-glossus, and two ligaments, 

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

 the levator palati, tensor tympani, and stapedius. 



SPHENOID BONE. The sphenoid (<r<pjv, 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 resemblance 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 ; pro- 

 ceeding 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. Pass- 

 ing 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 tubercles, the anterior clinoid 

 processes, which are the inner terminations of the lesser wings. Be- 

 neath these processes, on the sides of the olivary process, are two 

 depressions* for the last turn of the internal carotid arteries. Behind 

 the olivary process is the setta turcica (ephippium), the deep fossa 

 which lodges the pituitary gland and circular sinus ; behind and some- 

 what 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 Blumen- 

 bachii), which is continuous with the basilar process of the occipital 

 bone. On either side of the sella turcica is a broad groove (carotid) 

 which lodges the internal carotid artery, the cavernous sinus, and the 

 orbital nerves. Immediately external to this groove, at the junction 

 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, fourth, the three branches of the 



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

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

 clinoid process. 



