TEMPORAL BOXE. 



39 



twisted on itself so as to present an outer and inner surface, and a sharp 

 upper and lower border. The superior inargin is thinner, and p>rolonged 

 farther forward than the inferior. The bevelled extremioy 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 posforior root passes backwards, and is divided into two 

 parts, of which one turns inwards in front of the meatus externus, while 

 the other, gradually sul)siding, is 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 tnJjcrde, which gives attachment to the external lateral 

 ligament of the lower jaw. Between the two roots is the glenoid fossa, 

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

 the cylindrical elevation formed by the anterior root of the zygoma in 

 fi-ont of it, is coated with cartilage, and forms the concavo-convex 

 sin-face which articulates with the lower jaw. The fissure of Glaser 

 separates this articular part of the glenoid fossa from the remain- 

 ing part behind, which is formed by the tympanic plate of the petrous 

 division of the temporal bone, and lodges a jjart of the parotid gland. 



The mastoid portion is rough externally for the attachment of 

 muscles, and is prolonged downwards behind the aperture of tlie ear 

 into a nipple-shaped projection — the niasfoid process. This process has 

 on its inner side a deep groove, the digastric fossa, which gives attach- 

 ment to the digastric muscle ; and internal to that is the slight occiinicd 

 Siroovc, for the occipital artery. The internal surface of the mastoid 

 portion is marked by a deep sigmoid depression, which is part of the 

 groove of the lateral sinus. A passage for a vein, of very variable size, 

 the mastoid foramen, usually pierces the bone near its posterior margin, 

 and opens into the groove. 



Fig. S5. 



Fig. 33. — The Right Temporal Bone FROii 

 BELOW. (A. T.) 3 



The iudications where marked arc the same 

 as in the preceding figures. 14, is at tlie apex 

 of tiie jictrous bone in the upper opening of tlic 

 carotid canal ; 17, aqueduct of the cochlea ; 



21, lower rough surface of the petrous bone ; 



22, the lower openiug of the carotid canal ; 



23, the small foramen of Jacobson's nerve ; 



24, the jugular depression, and within it, 25, 

 the foramen of Arnold's nerve ; 26, stylo-mas- 

 toid foi'amen — the figure is placed in the ante- 

 rior part of the digastric groove ; 27, groove of 

 the occipital artery ; 28, place of the anterior 

 opening of the osseous Eustachian canal. 



The petrous portion is named 

 from its hardness. It contains the 

 organ of hearing. It forms a three- 

 sided pyramid, with its base directed 

 outwarcls, one surface looking down- 

 wards, and the other two turned 

 towards the interior of the skull. 



Inferior surface, base, and ajnx. — At fehe base is the aperture of the 



