THE SKULL AS A WHOLE 



133 



angle of the parietal bone, is named the pterion. This point is about on a level 

 with the external angular process of the frontal bone and about one and a half 

 inches (3.75 cm.) behind it. This fossa is deeply concave in front, convex 

 behind, traversed by grooves which lodge branches of the deep temporal arteries, 

 and filled by the Temporal muscle. 



The Mastoid Portion. The mastoid portion of the side of the skull is bounded 

 in front by the anterior root of the zygoma ; above, by a line which runs from the 

 posterior root of the zygoma to the end of the mastoparietal suture; behind and 

 below by the masto-occipital suture. It is formed by the mastoid and part of the 

 squamous and petrous portions of the temporal bone; its surface is convex and 

 rough for the attachment of muscles, and presents, from behind forward, the 

 mastoid foramen, the mastoid process, the external auditory meatus surrounded by 

 the tympanic plate, and, most anteriorly, the temporomaxillary articulation. The 

 point where the posterior inferior angle of the parietal meets the occipital and 

 mastoid portion of the temporal is named the asterion. 



Spheno-maxillary fissure 



Infra-temporal crest 



Pterygo-maxillary fissure 



Hamular process 



External auditory meatus' 

 Tympanic-plate 

 Styloid process 



Glenoid cavity 

 Zygomatic process (cut) 



External pterygoid plate 

 FIG. 100. Left zygomatic fossa. 



The Zygomatic Fossa (fossa infratemporalis). The zygomatic fossa is an irregu- 

 larly shaped cavity, situated below and on the inner side of the zygoma ; bounded in 

 front by the zygomatic surface of the maxilla and the ridge which descends from its 

 malar process; behind, by the posterior border of the external pterygoid plate and 

 the eminentia articularis; above, by the pterygoid ridge on the outer surface of the 

 greater wing of the sphenoid and the under part of the squamous portion of the 

 temporal ; below, by the alveolar border of the maxilla ; internally, by the external 

 pterygoid plate; and externally, by the zygomatic arch and ramus of the mandible 

 (Fig. 100). It contains the lower part of the Temporal, the External and Internal 

 pterygoid muscles, the internal maxillary artery and vein, and inferior maxillary 



