'22 PRACTICAL ANATOMY. 



is for the passage of the occipital artery. A section of 

 the mastoid process shows that it is cellular, and its cells, 

 which communicate with the tympanum, are lined by a 

 continuation of the tympanic mucous membrane. The 

 inner surface of the mastoid portion is deeply grooved 

 for the passage of the lateral sinus. In front of the 

 mastoid portion, and behind the middle root of the 

 zygoma, is the trumpet-shaped opening of the external 

 auditory meatus, surrounded by a rough ring of bone, 

 the auditory process, to which is attached the external 

 ear. The external auditory meatus is a canal which 

 passes slightly downward and forward to the tympanum, 

 from which it is separated by the membrana tympani. 

 The length of this canal in the bone is about three- 

 fourths inch. It is about one-fourth inch in diameter. 

 The glenoid fossa is a deep cavity in front of the ex- 

 ternal auditory meatus. It is bounded anteriorly by the 

 tubercle of the zygoma and the eminentia articularis; 

 posteriorly, by the middle root of the zygoma and the 

 vaginal process ; internally, by the vaginal process and 

 the eminentia articularis. It is about three-fourths 

 inch in depth, one-half inch antero-posteriorly, and is 

 crossed obliquely from behind, forward and downward, 

 by the Glasserian fissure, which begins just below the 

 middle root of the zygoma, and passes downward and 

 forward to the angle between the petrous and squamous 

 portions of the temporal bone. It communicates with 

 the tympanum, transmits the laxator tympani muscle 

 and the tympanic branch of the internal maxillary 

 artery, and lodges the processus gracilis of the malleus. 

 The canal of Hugier is just in front of the Glasserian 

 fissure, and transmits the chorda tympani nerve. The 

 roof and posterior wall of the glenoid fossa are trans- 

 lucent, and can be readily crushed in by a force projected 



