1054 



ORGANS OF SPECIAL SENSE 



otid (anterior) wall presents superiorly the tensor tympani muscle in its canal, and 

 the opening of the tuba auditiva (Eustachian tube) (fig. 751). Inferiorly, a thin, bony 

 wall, covered with tympanic cellulse and pierced by the carotico-tympanic nerves, 

 separates the tympanic cavity from the carotid canal. The membranous (lateral) 

 wall is formed mainly by the tympanic membrane, with the small rim of bone to 

 which it is attached, but superiorly the lateral wall of the epitympanic recess is formed 

 by bone. The labyrinth (medial) wall (fig. 749) presents ventrally the promontory, 

 with the tympanic plexus (Jacobson's nerve) lodged in grooves upon its surface. In- 

 ferior and posterior to the promontory is a depression or fossula at the bottom of 

 which is the cochlear fenestra (fenestra rotunda) , closed by the secondary tympanic 

 membrane, and posterior to the promontory is a smooth projection, the subiculum of 

 the promontoru, which forms the inferior border of a rather deep depression known as 

 the tympanic sinus. Superiorly is the cochkariform process, and superiorly and pos- 

 teriorly are a depression or fossula leading to the vestibular fenestra (fenestra ovalis), 



FIG. 749. THE LABYRINTH (MEDIAL) WALL OF THE RIGHT TYMPANUM WITH THE TYMPANIC 



OSSICLES IN POSITION. 



SHORT PROCESS OF INCUS : _ 



LONS PROCESS OF INCUS 

 CHORDA TYMPAN! 



FACIAL NERVE 



PYRAMIDAL EMINENCE 



Tendon of stapedius 

 STAPES 



COCHLEAR FOSSULA 



f 



Torn edge of mucoaa of 

 superior ligament of 

 incus 



BODY OF INCUS 



HEAD OF MALLEUS 

 NECK OF MALLEUS 



Anterior malleolar 



ligament 

 LATERAL PROCESS OF MALLEUS 



CHORDA TYMPANI 



Torn edge of tympanic 

 membrane 



MANUBRIUM OF MALLEUS 



TYMPANIC PLEXUS 

 PROMONTORY 



TYMPANIC CELLUL/E 



which is closed by the base of the stapes, the prominence of the facial (Fallopian) 

 canal, and the prominence of the laterat semicircular canal. 



The tympanic cavity contains three small movable bones, joined together and 

 to the walls of the cavity, and having attached to them special muscles and ligaments. 

 These auditory ossicles form a chain across the tympanic cavity, connecting the tym- 

 panic membrane and the vestibular (oval) fenestra. They are the malleus, the in- 

 cus, and the stapes, and are described on p. 69. 



Articulations of the ossicles. The manubrium and lateral process of the malleus are im- 

 bedded in the tympanic membrane, and an irregularly elliptical articular surface on the posterior 

 side of the head of the malleus is bound to the body of the incus by a thin capsular ligament, 

 forming a diarthrodial joint, the incudo-malleolar articulation. From the inner surface of the 

 capsular ligament, a wedge-shaped rim projects into the joint cavity and incompletely divides it. 

 The long crus of the incus is arranged parallel but dorsal and medial to the manubrium of the 

 malleus (figs. 749 and 751), and ends dorsally and superiorly to the tip of the manubrium in the 

 lenticular process. The convex extremity of this fits into the concavity on the head of the stapes, 

 to form a diarthrodial joint, the incudo-stapedial articulation. From its articulation with 

 the incus the stapes passes almost horizontally across the tympanic cavity to its junction 



