8o ELEMENTARY ANATOMY. [LESS. 



ear below, is continued inwards as a tube having on its under 

 surface a rough ridge. On account of its connexion with the 

 drum of the ear it is called " tympanic? and forms the floor 

 of the passage leading into the internal ear or meatus audi- 

 torius externus. Between it and the glenoid surface is a 

 narrow slit or fissure, called the fissura Glaseri (which trans- 

 mits the chorda tympani nerve), while behind it hangs down 

 a long, very slender process, termed "styloid," posterior to 

 and outside the root of which is the stylo-mastoid foramen, 

 which transmits the facial nerve. 



The rest of the bone consists of two parts, namely, (i) the 

 mastoid process already referred to, and (2) an irregularly 

 shaped piece (which on account of its hardness is called 

 the petrous 1 bone) projecting inwards like a wedge on the base 

 of the skull, between the occipital and the sphenoid. In 

 addition to the connexions already noted, the temporal joins 

 the malar by means of its zygomatic process. 



The petrous and mastoid portions enclose the inner and 

 essential parts of the ear, the internal canal of which (called 

 meatus auditorius interims} opens on the inner surface of the 

 petrous, wedgelike piece, and gives entrance to the nerve of 

 hearing. 



Towards the apex of the wedgelike projection is seen a 

 large aperture which is one end of a canal, the other end of 

 which opens on the under surface within and in front of the 

 styloid process. This is the canal for the internal carotid 

 artery, which thus takes its way right through the petrous 

 portion of the temporal bone. Internal to its anterior open- 

 ing and at the angle formed by the junction of the petrous 

 part of the temporal bone with its squamous part, are two 

 small openings placed one above the other. These are the 

 apertures of two tubes (which run backwards, parallel and 

 apposed like the barrels of a double-barrel gun, in the sub- 

 stance of the bone), the lower of which is the Eustachian 

 tube, and conveys air from the mouth to the internal ear. The 

 upper tube gives passage to the small tensor tympani muscle. 

 A sharp ridge runs inwards and forwards from the root of 

 the styloid process. This ridge is termed the vaginal process. 



The temporal bone arises by very distinct and significant 

 ossifications. 



Thus we have (i) the squamous and zygomatic portions 

 forming one element ; (2) the tympanic portion, which is at 

 first a mere delicate ring of bone ; (3) the styloid process, 



1 From Tre'rpof, a stcne. 



