;o A MANUAL OP ANATOMY 



zygoma ; the mastoid portion ; and the petrous portion^ which 

 bears inferiorly the styloid process. 



The squamous portion (squamo-zygomatic) hes almost vertically, 

 and presents two surfaces, outer and inner, and a superior border. 

 The outer surface is convex towards its centre, and forms a large 

 part of the temporal fossa. It gives origin to fibres of the temporal 

 muscle, and is marked by a groove for the middle temporal artery, 

 which extends upwards and slightly forwards from a point just 

 above the external auditory meatus to the superior border. The 

 inner surface, which is concave, is related to the temporo-sphenoidal 

 lobe of the cerebrum, and presents a few digitate impressions and 

 meningeal grooves. The superior border is much arched, and 

 describes about two- thirds of a circle. Except over the lower 

 part of its anterior portion, it is markedly bevelled at the expense 

 of the inner plate for the parietal, which it overlaps. Anteriorly 

 over its lower part it is thick and serrated for the external border 

 of the great wing of the sphenoid. The place of junction of the 

 squamous and petrous portions is indicated at the lower part of 

 the inner surface of the former by the narrow petro-squamous 

 groove or suture. 



The zygoma (jugal process) springs from the lower part of the 

 outer surface of the squamous portion. Its base is compressed 

 from above downwards, and directed outwards. It then under- 

 goes a twist, and is directed forwards in a curved manner, being 

 laterally compressed. This part of it presents two borders, two 

 surfaces, and an extremity. The superior border, sharp and convex, 

 extends farther forwards than the inferior, and gives attachment 

 to the temporal fascia in two divisions. The inferior border gives 

 origin to fibres of the masseter. The outer surface is convex and 

 subcutaneous, whilst the inner, which is concave and looks towards 

 the upper part of the zygomatic fossa, gives origin to fibres of the 

 deep part of the masseter. The extremity is bevelled at the expense 

 of the lower border, and serrated for the malar. The base of the 

 zygoma presents two roots, anterior and posterior. The anterior 

 root, which is continuous with the inferior border of the process, 

 is directed inwards in front of the glenoid fossa. It is at first 

 narrow, but subsequently thick and convex, where it is covered by 

 cartilage. This portion is called the eitiinentia articularis, and in 

 front of it there is a small triangular area which looks into the 

 zygomatic fossa. The posterior root, which is continuous with the 

 superior border of the process, passes backwards above the external 

 auditory meatus, then between the squamous and mastoid portions, 

 where it is known as the supramastoid crest, and finally it turns 

 upwards, where it forms part of the posterior boundary of the 

 temporal fossa. In front of the external auditory meatus it sends 

 downwards a short offshoot, which lies between the external audi- 

 tory meatus and the anterior part of the glenoid fossa. This is 

 called the postglenoid process, and is sometimes referred to as the 

 middle root of the zygoma. 



