1038 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 



The tympanic cavity consists of two parts: the tympanic cavity proper, opposite 

 the tympanic membrane, and the attic or epitympanic recess, above the level of 

 the membrane; the latter contains the upper half of the malleus and the greater 

 part of the incus. Including the attic, the vertical and antero-posterior diameters 

 of the cavity are each about 15 mm. The transverse diameter measures about 

 6 mm. above and 4 mm. below; opposite the center of the tympanic membrane 

 it is only about 2 mm. The tympanic cavity is bounded laterally by the tympanic 

 membrane; medially, by the lateral wall of the internal ear; it communicates, 

 behind, with the tympanic antrum and through it with the mastoid air cells, and 

 in front with the auditory tube (Fig. 907). 



The Tegmental Wall or Roof (paries tegmentalis) is formed by a thin plate of bone, 

 the tegmen tympani, which separates the cranial and tympanic cavities. It is 

 situated on the anterior surface of the petrous portion of the temporal bone close 

 to its angle of junction with the squama temporalis; it is prolonged backward so 

 as to roof in the tympanic antrum, and forward to cover in the semicanal for the 

 Tensor tympani muscle. Its lateral edge corresponds with the remains of the 

 petrosquamous suture. 



The Jugular Wall or Floor (paries jugularis) is narrow, and consists of a thin plate 

 of bone (fundus tympani) which separates the tympanic cavity from the jugular 

 fossa. It presents, near the labyrinthic wall, a small aperture for the passage of 

 the tympanic branch of the glossopharyngeal nerve. 



Post, malleolar fold 

 Long crus of incus 



Manubrium 

 of malleus 

 Postero-superior 

 quadrant 



Postero-inferior 

 quadrant 





Lat 



. proc. of malleus 

 Ant. malleolar fold 



Antero-superior 



quadrant 

 Umbo 



Cone of light 



Antero~inferior quadrant 

 FIG. 909. Right tympanic membrane as seen through a speculum. 



The Membranous or Lateral Wall (paries membranacea; outer wall) is formed 

 mainly by the tympanic membrane, partly by the ring of bone into which this 

 membrane is inserted. This ring of bone is incomplete at its upper part, forming 

 a notch (notch of Rivinus), close to which are three small apertures: the iter chordae 

 posterius, the petrotympanic fissure, and the iter chordae anterius. 



The iter chordae posterius (apertura tympanica canaliculi chorda) is situated in 

 the angle of junction between the mastoid and membranous wall of the tympanic 

 cavity immediately behind the tympanic membrane and on a level with the upper 

 end of the manubrium of the malleus; it leads into a minute canal, which descends 

 in front of the canal for the facial nerve, and ends in that canal near the stylo- 

 mastoid foramen. Through it the chorda tympani nerve enters the tympanic 

 cavity. 



The petrotympanic fissure (fissura petrotympanica; Glaserian fissure) opens just 

 above and in front of the ring of bone into which the tympanic membrane is 

 inserted; in this situation it is a mere slit about 2 mm. in length. It lodges 

 the anterior process and anterior ligament of the malleus, and gives passage to the 

 anterior tympanic branch of the internal maxillary artery. 



