THE TEMPORAL BONE. 



41 



TEMP. SUBF. 



ZYCOM. SURF. 



PETROUS PORTION 



EUST. CANAL 



INF. PETR. SUUCUS 



from without inwards, and divided into two parts by the nearly transverse fissure 

 of Glaser. The posterior part of the glenoid fossa is formed by the tympanic plate 

 of the petrous division of the bone, is non-articular, and lodges a portion of the 

 parotid gland : the anterior part of the fossa, together with the cylindrical elevation, 

 articular eminence, formed by the anterior root of the zygoma in front of the hollow, 

 is coated with cartilage, 



and forms the concavo- SQUAMOUS PORTION 



convex surface for arti- 

 culation with the lower 

 jaw ; the articular cavity 

 is bounded behind by 

 a small conical process 

 which descends in front 

 of the external auditory 

 meatus, and is known as 

 the postf/lcnoid process. 

 In front of the articular 

 eminence, and separated 

 from the temporal sur- 

 face by a slight ridge, is 

 a small triangular area 

 which enters into the 

 zygomatic fossa. 



The mastoid por- 

 tion is rough externally 

 for the attachment of 

 muscles, and is prolonged 

 downwards behind the 

 aperture of the ear into 

 a nipple-shaped projec- 

 tion the mastoid pro- 

 cess. This process has 

 on its inner side a deep 

 groove,the digastricfossa, 

 which gives attachment 

 to the digastric muscle 

 occipital artery. 



AQ. OF COCHL. 



MAST. PROC 



MASTOID PORTION 



Fig. 42. RIGHT TEMPORAL BONE, FROM BELOW. (Drawn by D. Gunn.) 



and internal to that is the slight occipital groove, for the 

 The internal surface of the mastoid portion is marked by a deep 

 sigmoicl 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. 



The petrous portion, so named from its hardness, contains the organ of 

 hearing. It forms a three-sided pyramid, with its base directed outwards, one 

 surface looking downwards, and the other two turned towards the interior of the 

 skull. 



Inferior surface, base, and apex. At the base is the aperture of the ear. It 

 forms a short canal, the external auditory meatus, directed inwards and a little 

 forwards, narrower in the middle than at its extremities, and leading into the cavity 

 of the tympanum, part of which is seen from the exterior in the macerated bone. 

 The external orifice is bounded above by the posterior root of the zygoma, and in 

 the remainder of its circumference chiefly by the external auditory process, a curved 

 uneven border, to which the cartilage of the ear is attached. This process is the 

 thickened outer extremity of the tympanic plate, a lamina one surface of which 

 forms the anterior and inferior wall of the external auditory meatus and the 



