THE TEMPORAL BONES. 21 



extremity of which is serrated for articulation with the 

 malar bone. The zygoma arises from the side of the 

 temporal bone by three roots. The posterior root is the 

 temporal ridge ; the middle root passes down in front of 

 the external auditory meatus, limiting the glenoid fossa 

 posteriorly ; the anterior root forms a well-marked tu- 

 bercle, which passes downward and inward in front of 

 the glenoid fossa, and becomes lost in the eminentia 

 articularis. The superior border of the zygoma is long, 

 thin, and sharp, and has attached to it the two leaflets 

 of the temporal aponeurosis. The inferior border, 

 shorter than the superior, thick and rounded, forms two 

 arches, the first between the extremity and the tubercle. 

 This arch affords attachment to the masseter muscle. 

 The second arch, deeper and much shorter than the 

 first, is between the anterior and the middle roots of the 

 zygoma, and assists in forming the roof of the glenoid 

 fossa. 



The internal surface of the squamous portion is 

 marked by depressions for the convolutions of the brain, 

 and grooved along its posterior portion by the middle 

 meningeal artery. 



The mastoid portion is behind and below the tem- 

 poral ridge. It articulates superiorly with the parietal 

 bone, and posteriorly with the occipital. Its borders are 

 broad and blunt, posteriorly slightly serrated. It is a 

 rough, bulky process of bone, terminating inferiorly in 

 a tubercle called the mastoid process. In the posterior 

 border is the mastoid foramen, which is sometimes 

 placed in the suture between the mastoid portion and the 

 occipital bone. The inferior portion of the mastoid 

 process presents two grooves upon its inner face. The 

 external, or digastric, is for the attachment of the digas- 

 tric muscle ; the inner groove not so strongly marked, 



