OSSA TEMPORUM. 67 



parts of the cranium ; each of them is divided into three portions, 

 a superior or squamous, a posterior or mastoid, and a middle or 

 petrous. 



The squamous portion is nearly semicircular in form, and 

 very thin ; its edge is sharp, and the inner table appears pared 

 away to form the squamous suture with the corresponding 

 edge of the parietal bone. Its external surface is covered by 

 the temporal muscle. At the lower and anterior part of this 

 surface, the zygomatic process arises, it proceeds forward to 

 join the cheek bone, and form an arch under which the tem- 

 poral muscle passes. 



At the base of the process is the glenoid cavity for the condyle 

 of the lower jaw. Immediately before this cavity is a tubercle 

 or protuberance, near the commencement of the zygoma and 

 at its lower border, to which the external lateral ligament of 

 the lower jaw is attached ; continued horizontally inwar-ds 

 from the tubercle there is a rounded eminence, called the emi- 

 nentia articularis, which forms part of the articular surface on 

 which the condyle rises when the jaw is opened. In the pos- 

 terior part of the cavity is a fissure — called the glenoid — in 

 which part of the ligament of this articulation is fixed. In 

 ■this fissure is an aperture — glenoid foramen — which communi- 

 cates with the cavity of the tympanum of the ear, and is occu- 

 pied by a small nerve called chorda tympani ; and also by the 

 anterior muscle of the malleus — one of the small bones of the 

 ear. 



The internal surface of the squamous portion is concave ; it 

 is marked by pits and small eminences, which correspond with 

 the convoluted surface of the brain, and also by impressions of 

 the arteries of the dura mater, see 4 fig. 13, as they go towards 

 the parietal bone. 



The mastoid or occipital portion is the smallest of the three 

 parts of the bone ; it consists of an angular portion, which 

 occupies a vacuity between the occipital and parietal bones; 

 and of the mastoid process. The mastoid process has some 

 resemblance to the nipple; it is composed internally of cells 

 which communicate with the cavity of the tympanum. On 



