72 . A MANUAL OF ANATOMY 



Glaserian fissure, and is formed by the tympanic plate, which 

 separates it from the external auditory meatus. It is shallow, 

 non-articular, and quadrilateral, and it lodges the deep part of the 

 parotid gland. 



The fissure of Glaser, which is the remains of the petro-tympanic 

 fissure, is closed in its outer part, and is divided into two internally 

 by means of a thin plate which descends from the tegmen tym- 

 pani, and forms the chief part of the outer wall of the canals for 

 the osseous part of the Eustachian tube and tensor tympani 

 muscle. Between this plate and the tympanic plate the processus 

 gracilis of the malleus is located internally, and there is a small 

 opening leading to the tympanic cavity for the passage of the 

 tympanic branch of the internal maxillary artery and the anterior 

 ligament of the malleus (so-called laxa'.or tympani muscle) or band 

 of Meckel. At the inner end of the Glaserian fissure is another 

 minute opening leading from the tympanic cavity, called the canal 

 of Huguier, or iter chordae anterius, which transmits the chorda 

 tympani nerve. 



The mastoid portion is so named from the mastoid process which 

 it bears. It is limited above by the supramastoid crest and its 

 own superior border, in front by the external auditory meatus and 

 auricular or tympano-mastoid fissure, and behind by its posterior 

 border. It presents two surfaces and two borders. The external 

 surface, rough and convex, is prolonged downwards behind the 

 external auditory meatus into the mastoid process, which presents 

 on its inner surface two grooves. The outer, called the digastric 

 groove, is deep, and gives origin to the posterior belly of the 

 digastric ; and the inner, called the occipital groove, is narrow, and 

 lodges the occipital artery. The upper part of the outer surface of 

 the mastoid process gives origin over its posterior half to the 

 retrahens auriculam and part of the occipitalis, in this order from 

 before backwards ; and lower down, it gives insertion to the sterno- 

 cleido-mastoid, splenius capitis, and trachelo-mastoid, in this order 

 from above downwards. At the upper and back part of the 

 mastoid portion, a little below the supramastoid crest, there may 

 be the remains of the squamo-mastoid suture directed downwards 

 and forwards, indicating the line of junction of the squamo-zygo- 

 matic and basal part of the petrous portions. Directly in front 

 of the root of the mastoid process there is an important depressed 

 area, called the suprameatal triangle (Macewen), which is bounded 

 as follows : above by part of the posterior root of the zygoma, below 

 by the postero-superior part of the external auditory meatus, and 

 behind by a vertical line connecting the upper and lower boundaries, 

 which line is continuous with the posterior part of the external 

 auditory meatus. In the lower part of the suprameatal triangle 

 is the suprameatal spine, a sharp, antero-posterior scale of bone, 

 which gives attachment to a portion of the cartilage of the external 

 ear. The outer surface of the mastoid portion presents several 

 small nutrient foramina, and often there is a large opening, called 



