THE SKULL THE CRANIUM 195 



quarter it is the continuation inward, toward the middle line, of the 

 glenoid cavity, and its inner edge is rough, bevelled, and overlapped 

 by the alisphenoid. In the rest of its extent three narrow regions 

 may be distinguished, namely, () an outer region, which lies outside 

 the auditory nieatus ; (b) a middle region, which enters into the forma- 

 tion of the rim of the auditory meatus ; and (c) an inner region, which 

 lies within the auditory meatus and enters into the formation of the 

 tympanum. 



(a) The Outer Region. The surface behind the postglenoid 

 process on the outside arches upward as the under surface of the 

 posterior root of the zygoma. This part is wider in front than 

 behind, where it fades out on the outer surface of the mastoid. Its. 

 outer margin is emarginate for the anterior half and nearly straight 

 behind. It is concave from side to side as well as from before back- 

 ward, and faces downward and outward. 



(b) The Middle Region. On the inner side of the anterior end 

 of the under surface of the zygomatic root, just behind the post- 

 glenoid foramen, is a depressed oval area, whereof the long axis 

 is directed obliquely backward and inward. Its posterior part is 

 rough, where the anterior end of the ectotympanic of the bulla is 

 attached. Behind this area is a rounded ridge, which arches slightly 

 upward and is directed outward and backward, sometimes straight, 

 sometimes emarginate externally. It forms the middle part of the 

 upper margin of the external auditory meatus, while all the rest of 

 the bone surrounding the orifice is contributed by the ectotympanic 

 of the bulla. This middle region terminates behind in a circular, 

 roughened point of attachment for the posterior upper end of the 

 ectotympanic. Behind this point, and separating the lower surface of 

 the squamous from the mastoid process, is a transverse groove, which, 

 meeting a notch in the bulla between the ends of the ectotympanic 

 and entotympanic, is converted into the stylomastoid foramen. 



(c) The Inner Region. The strip which is within the margin 

 of the auditory meatus consists of three parts. In front, just within 

 the oval depression for the attachment of the ectotympanic, is a 

 small area, wider in front than behind, and bounded in front by a 

 line drawn inward from the postglenoid process, on the outside by 

 the elevated oblique inner margin of the oval depression, and on 

 the inside by a straight, longitudinal, serrated border, which is 



