40 OSTEOLOGY, OR ANATOMY OF OSSEOUS SYSTEM 



of a circle. The outer surface is vertical, with a slight convexity, 

 and forms a part of the temporal fossa. This portion over- 

 laps the mastoid behind. Above the aperture of the ear is 

 a vertical groove for the middle temporal artery. 



The zygoma is connected with the lower and outer part of 

 the squamous portion; it is broad at its base, with surfaces 

 looking up and down; it then twists on itself, so that it has 

 inner and outer surfaces, upper and lower borders. The upper 

 border is thin and longer than the inferior, which is short and 

 arched; the anterior extremity articulates with the zygomatic 

 process of the malar bone, overlapping it. The zygoma is 

 attached by two roots; the anterior, continuous with the lower 

 border, is a broad convex ridge directed inward, called the 

 emincntia articularis. At the junction of this W'ith the zygoma 

 is a tubercle for the external lateral ligament of the lower jaw. 

 The posterior root prolongs the upper border of the zygoma 

 as the supramastoid crest, which becomes continuous with 

 the lower temporal line; it is above the suture between the 

 squama and mastoid. Between the two roots is the glen old 

 fossa; its articular portion is bounded behind by the post- 

 glenoid process, sometimes called the middle root of the zygoma. 

 It is strongly developed in some mammals to prevent posterior 

 dislocation of the lower jaw. The inferior axjji'cf of the hori- 

 zontal portion presents three districts the auricular, articular, 

 and zygomatic, from behind forward. The auricular part 

 forms the upper concave margin of the external auditory 

 meatus and a part of the roof of the external ear. The next, 

 portion is the glenoid fossa, which is divided into two parts 

 by the transverse fissure of Glaser, which is a double cleft. 

 The posterior part is non-articular, formed by the tympanic 

 plate and lodging part of the parotid gland. The anterior 

 part of the fossa is articular, bounded behind by the post- 

 glenoid process and in front by the eminentia articularis; 

 it is the fossa mandibularis, concavoconvex for the condyle 

 of the lower jaw. The first fissure behind the articular fossa 

 is the petrosquamous, next comes a narrow projection of the 

 tegmcn tympani from the petrous, and next the petrotympanic 

 fissure or Glaserian fissure proper; it lodges the slender process 

 of the malleus and tympanic branch of the internal maxillary 

 artery. Farther in, and external to the Eustachian tube, is 

 the canal of Huguier, by which the chorda tympani nerve 



