THE TEMPOEAL BONE. 



39 



with the parietal bones in the coronal suture in the manner before described ; the 

 lower transverse part is thin and uneven, and articulates with the greater and lesser 

 wings of the sphenoid. 



Varieties. The trochlear fossa is often faintly marked or absent ; on the other hand 

 there may be a small prominence, thetj-ochlcar sjjine. by the side of the depression (10 percent.. 

 3Ierkel). The frontal bone is at times divided by a median frontal or metopic suture, the two 

 parts of the infantile bone having failed to unite. This condition, which is termed utctopism, 

 was found by Anutschin to exist in 8'7 per cent, of European skulls, in 5'1 per cent, in Mon- 

 golian races, in 1'2 per cent, of Negro, and 1 per cent, of Australian skulls. A trace of the 

 metopic suture is to be seen in nearly all adult frontal bones above the root of the nose (fig. 36). 



THE TEMPORAL BONE. 



The temporal bone takes part in the formation of the side and base of the skull, 

 and contains in its interior the organ of hearing. It is usually described in three 

 parts, viz., an expanded* anterior and superior part, the sqiiamous portion, including 



SQUAMOUS PORTION 



TEMP. SUHF. 





MASTOID PORTION 



Fig. 40. RIGHT TEMPORAL BONE: OUTER VIEW. (Drawn by D. Gunn.) 



the zygomatic process, a thicker posterior portion, the mastoid, and below and 

 between these the petrous portion, a three-sided pyramid, exhibiting at its base 

 externally the aperture of the ear, and projecting forwards and inwards into the base 

 of the skull. 



It articulates posteriorly and internally with the occipital bone, superiorly with 

 the parietal, anteriorly with the sphenoid, by the zygomatic process with the malar, 

 and by the glenoid cavity with the inferior maxillary bone. 



The squamous portion, or squamo-zygomatic, extends forwards and upwards 

 from its connection with the other portions, and is limited superiorly by an arched 

 border which describes about two-thirds of a circle. 



