23 2 THE POCKET ANATOMY 



The posterior wall presents above the large aperture of the 

 mastoid antrum (aditus ad antrum} and below : 



The pyramid which is placed just behind the fenestra ovalis ; 

 it contains the stapedius, the tendon of which projects through 

 the apex. 



The anterior wall shows the following : 



The canal for the tensor tympani, opening just anteriorly to 

 the fenestra ovalis. 



The processus cochleariformis : a process of bone lying be- 

 tween and separating the canal for the tensor tympani and 

 the Eustachian tube. 



The Eustachian tube leads into the pharynx, is partly carti- 

 laginous and partly osseous ; the internal or cartilaginous part 

 is trumpet-shaped, and terminates in an oval opening at the 

 side and upper part of the naso-pharynx. The osseous portion 

 is placed along the angle of union of the squamous and petrous 

 portions of the temporal bone, and is about inch long. 

 Below this a thin plate of bone separates the tympanum 

 from the carotid canal. 



The membrana tympani is the membrane which separates 

 the external and middle ears. It is inserted into the groove 

 in the osseous portion of the external meatus, and is placed 

 obliquely across the opening, forming with the floor of the 

 meatus an angle of 45. It contains the handle of the malleus 

 between its layers, which makes the membrane concave ex- 

 ternally. There is a small notch in the upper and anterior 

 part of the groove of insertion known as the notch of Rivini, 

 which is closed by a loose portion of the membrane, the 

 membrana ftaccida of Shrapnell. 



Structure of the membrane, from without inwards: 



1. Prolongation of skin of meatus. 



2. Fibrous tissue or membrana propria. 



3. Mucous membrane of the tympanum. 



The ossicles of the tympanum are : 



1. The Malleus. 



2. The Incus. 



3. The Stapes. 



The malleus, or hammer, consists of : 



The head: the thickened upper part, presenting on tne 

 posterior surface a facet for articulation with the body of the 

 i-icus. 



The neck : a constriction below the head. 



