I500 



HUMAN ANATOMY. 



orbicular process and the capsular ligament. The tendon is frequently enveloped in a fold of 

 mucous membrane. A branch of the facial nerve passes through a small orifice between the 

 Fallopian canal and the canal for the stapedius to supply this muscle. 



Movements of the Ossicles. — When the tympanic membrane and malleus-handle are moved 

 inward, the long process of the incus is also moved inward and pushes the head of the stapes 

 inward, and slightly upward. This causes pressure upon the liquid within the labyrinth, and, 

 since the bony walls of the labyrinth are inelastic, the membrane of the round window is bulged 

 outward. As the tympanic membrane regains its normal position, these movements are re- 

 versed. When on the other hand the tympanic membrane is moved outward, the movement of 

 the long process of the incus is very slight because of the unlocking of the malleo-incudal articu- 

 lation. Contraction of the tensor tympani muscle draws the centre of the tympanic membrane 

 inward and in this way increases the tension of the membrane and of the posterior part of 

 the axial ligament of the malleus, especially of its external portion. Contraction of the stapedius 

 muscle pulls the head of the stapes backward, thus tilting the anterior end of the foot-plate out- 

 ward, the posterior end acting as a fulcrum. 



The Mucous Membrane of the Tympanum. — The tympanic cavity is 

 lined by a thin transparent mucous membrane, closely adherent to the periosteum 

 and continuous with that of the Eustachian tube and naso-pharynx anteriorly, and 



stapedius 

 muscle 



Posterior crus of 

 stapes 



Vestibule 



Footplate of -c^j 

 stapes 



Internal audito- 

 ry canal 



Vestibular 

 ganglion 



Cochlear nerve 



Basal turn of 

 cochlea 



Stapedius 

 tendon 



Tympanic 

 membrane 



Lower end of 

 incus 



Malleus handle 



Tjinpanic cavitj 



Horizontal section through human middle and internal ear; stapes occludes oval window. X 5!4. Drawn from 



preparation made by Dr. Ralph Butler. 



with that of the mastoid cells posteriorly. It covers the ossicles and their ligaments, 

 the muscles, the tendons and the chorda tympani nerve, and forms a number of folds 

 extending across the cavity. These folds vary in location, direction and number, 

 and form pouches within the tympanum. 



The attic is divided into an external and an internal compartment by the incus, 

 the head of the malleus, the superior ligament of the malleus and the superior malleo- 

 incudal fold of mucous membrane. The external compartment is bounded on the 

 outer side by the external tympanic wall, and is itself subdivided into a superior and 

 an inferior space by the external ligament of the malleus. The inferior division is 

 called Prussak's space and is bounded externally by Shrapnell's membrane, inter- 

 nally by the neck of the malleus, inferiorly by the short process of the hammer, and 

 superiorly by the external ligament of the malleus (Fig. 1258). A number of 



