THE TYMPANIC CAVITY 



1089 



a large irregular space into which open the mastoid cells (see p. 1092). The boundaries of the 

 orifice are formed above by the tegmen tympani, medially by the prominences of the lateral 

 semicircular canal and facial nerve, and laterally by a plate of bone termed the scutum. 



The carotid (anterior) wall presents superiorly the tensor tympani muscle in its canal, 

 and at a lower level the opening of the tuba auditiva (Eustachian tube) (fig. 835). Inferiorly, 

 a thin, bony wall, covered with tympanic cellute 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 a plate of bone termed the scutum. 



The labyrinth (medial) wall (fig. 833) presents inferiorly the promontory, produced by the 

 first turn of the cochlea with the tympanic plexus (Jacobson's nerve) lodged in grooves upon its 

 surface. Inferior and posterior to the promontory is a depression or fossula at the bottom of 



Fig. 833. — The Labyrinth (Medial) Wall of the Right Tympanum with the Tympanic 



Ossicles in Position. 



Short process of incus 



Long process of incus 



Chorda tympani 



Facial nerve 



Pyramidal 



eminence 



Tendon of 



stapedius 



Stapes 



Cochlear fossula 



Torn edge of mucosa 

 of superior liga- 

 ment 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 cellulae 



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

 and posterior to the promontory is a smooth projection, the svbiculum of the promontory, which 

 forms the inferior border of a rather deep depression known as the tympanic sinws. Anteriorly 

 and superiorly is the cochleariform process, and superiorly and posteriorly are a depression or 

 fossula leading to the vestibular fenestra {fenestra ovalis), which is closed by the base of the stapes, 

 the prominence of the facial (Fallopian) canal, and the prominence of the lateral semicircular 

 canal, the two latter being formed in the medial wall of the entrance to the mastoid antrum. 



The tympanic mucous membrane forms a complete covering for the walls and 

 contents of the tympanic cavity. It is continuous anteriorly with the mucosa of 

 the tuba auditiva (Eustachian tube) and posteriorly with that of the tympanic 

 (mastoid) antrum and mastoid cells. It is a thin, transparent, vascular membrane 

 intimately united to the periosteum. As it passes from the walls to the contents of 

 the tympanic cavity, besides covering the ligaments of the malleus and the incus 

 and the tendons of the tensor tympani and stapedius muscles, it forms a number of 

 special folds and pouches. 



The anterior malleolar fold is reflected fi*om the tympanic membrane over the anterior 

 process and ligament of the malleus and the adjacent part of the chorda tympani, and the 

 posterior malleolar fold stretching between the manubrium and the posterior tympanic wall, 

 surrounds the lateral ligament of the malleus and the posterior part of the chorda tympani. 

 Each of these folds presents inferiorly a concave free border, and between them and the tym- 

 panic membrane are two blind pouches, the anterior and posterior malleolar recesses or pouches 

 69. 



