36 



BONES OF THE HEAD. 



beyond the inner, forming a thin scale with the rough surface looking 

 inwards and overlapping the corresponding bevelled edge of the parietal 

 bone. But in front the border is thicker, looks directly forwards, and is 

 serrated for articulation with the great wing of the sphenoid boue. 



The outer surface is in its greatest extent vertical, with a slight con- 

 vexity, and formj part of the temporal fossa. From its lowest part a long 

 process, the zygoma, takes origin. 



The zygoma, or zygomatic process, is at its base of considerable breadth, 

 and projects outwards. It then becomes narrower, and is twisted on itself 

 so as to present an outer and inner surface, and a sharp upper and lower 

 border. The superior margin is the thinnest, and is prolonged furthest 

 forwards. The bevelled extremity is serrated, and articulates with the malar 

 bone. At its base the zygomatic process presents two roots. The anterior 

 root is a broad convex ridge, directed inwards. The posterior root passes 

 backwards, and is divided into two parts, of which one turns inwards in 

 front of the meatus externus, while the other, gradually subsiding, ia 

 continued backwards over that opening, and marks behind it the line of 

 union of the squamous and mastoid portions of the bone. At the point of. 

 division of the two roots is a slight tubercle, which gives attachment to 

 the external lateral ligament of the lower jaw. Between them is the glenoid 

 fossa, a depression elongated from without inwards, and which, together with 

 a cylindrical elevation on the anterior root of the zygoma in front of it, 

 is coated with cartilage, and forms the articular surface for the joint with 

 the lower jaw. The fissure of Glaser separates this articular part of the 

 glenoid fossa from the remaining part behind, which is formed by the 

 tympanic plate of the petrous division of the temporal bone and lodges a 

 portion of the parotid gland. 



Fig. 33. 



Fig. 33. THE RIGHT TEM- 

 PORAL BONE PROM THE 

 INNER SIDE. | 



The indications where 

 marked are the same as in 

 the preceding figure. 11, the 

 inner or cerebral surface of 

 the squamous portion ; 11 x , 

 the squamous edge ; 12, inner 

 surface of the mastoid por- 

 tion ; 13, the sigmoid groove 

 of the lateral sinus the 

 figure is placed at its upper 

 part, and close to the mastoid 

 foramen ; 14, the apex of the 

 petrous bone; 15, the meatus 

 auditorius internus; 16, the 

 scale of bone covering the 

 aqueduct of the vestibule; 

 17, is above the aqueduct of 

 the cochlea ; 18, the superior 

 petrosal groove ; 19, the 

 eminence of the superior 

 semicircular canal; 20, the 

 hiatus Fallopii. 



The MASTOID POUTION is rough externally for the attachment of muscles, 

 and is prolonged downwards behind the aperture of the ear into a nipple- 

 sliaped projection the mastoid process. This process has on its inner side 

 a deep groove, the digastric fossa t which gives attachment to the digastric 



3* 



