842 THE OEGANS OF SENSE. 



posterior end towards the labyrinth, thus rendering tense the ligamentum annulare 

 the lateral movement of the anterior end of the base being greater than the 

 medial movement of its posterior end. The muscle is supplied by the facial nerve. 



Movements of the Auditory Ossicles. The manubrium mallei follows all the 

 movements of the membrana tympani, while the malleus and incus move together around 

 an axis extending forwards through the crus breve of the incus and the anterior 

 ligament of the malleus. When the membrana tympani moves medialwards it carries with 

 it the manubrium mallei, while the incus, moving medialwards at the same time, forces the 

 base of the stapes towards the labyrinth. This movement is communicated to the fluid 

 (perilymph) in the labyrinth, and causes a lateral bulging of the secondary tympanic 

 membrane, which closes the fenestra cochleae. These movements are reversed when the 

 membrana tympani is relaxed, unless the lateral movement of the membrane is excessive. 

 In such a condition the incus does not follow the full movement of the malleus, but 

 merely glides on this bone at the incudo-malleolar joint, and thus the forcible dragging 

 of the base of the stapes out of the fenestra vestibuli is prevented. The cog-tooth 

 arrangement, already described, on the head of the malleus and body of the incus, causes 

 the incudo-malleolar joint to become locked during the medial movement of manubrium 

 mallei, the joint becoming unlocked during its lateral movement. 



Tunica Mucosa Tympanica. The mucous lining of the tympanic cavity is 

 continuous, through the auditory tube, with that of the nasal part of the pharynx ; 

 it extends backwards also and lines the tympanic antrum and the mastoid air-cells. 

 Thin, transparent, and closely united with the subjacent periosteum, it covers the 

 medial surface of the membrana tympani and is reflected over the auditory ossicles 

 and their ligaments. It also supplies sheaths for the tendons of the tensor tympani 

 and stapedius muscles, and forms the following folds, viz. : (a) one from the roof of 

 the recessus epitympanicns to the head of the malleus and body of the incus; 

 (5) one enveloping the chorda tympani nerve and crus longum of the incus ; (c) two 

 extending from the processus lateralis mallei one to. the anterior, the other to the 

 posterior margin of the notch of Kivinns. A recess, the pouch of Prussak, is situated 

 between the membrana flaccida and the neck of the malleus. Communicating 

 behind with the tympanic cavity, this pouch may serve as a reservoir to confine 

 pus or other fluid, since its opening into the tympanic cavity is above the level 

 of its floor, a condition analogous to the opening from the maxillary sinus into the 

 nasal cavity. The fold of mncous membrane which extends downwards to envelop 

 the chorda tympani nerve gives rise to two pouches, one in front of, and the other 

 behind, the manubrium mallei ; these are named the anterior and posterior recesses 

 of Troltsch. The epithelium which lines the mucous membrane is flattened over the 

 membrana tympani, promontory, and auditory ossicles, but ciliated and columnar 

 over the greater portion of the rest of the cavity. 



Vessels and Nerves of the Tympanic Cavity. The arteries supplying the tympanic 

 cavity are : (1) The anterior tympanic artery, a branch of internal maxillary, which reaches the 

 cavity by way of the petro-tympanic fissure. (2) The stylo-mastoid branch of posterior auricular, 

 which passes through the stylo-mastoid foramen and the facial canal ; it supplies branches to the 

 tympanic antrum and mastoid air-cells, to the stapedius muscle, to the floor and medial wall of 

 the tympanic cavity, and forms an anastomotic circle, around the membrana tympani, with the 

 anterior tympanic artery. (3) The middle meningeal artery sends a branch to the tensor tympani 

 muscle, and, after entering the skull, gives off its petrosal artery, which is conducted to the 

 tympanic cavity along the hiatus canalis facialis ; some twigs from the posterior division of the 

 middle meningeal reach the tympanic antrum and epitympanic recess through the petro- 

 squamous fissure. (4) The internal carotid artery, in its passage through the canal in the 

 temporal bone, gives off one or two tympanic twigs, while (5) a branch from the ascending 

 pharyngeal accompanies the tympanic nerve. The veins drain into the pterygoid plexus, and the 

 superior petrosal sinus. The lymph vessels form a network in the mucous membrane and end 

 mainly in the retro-pharyngeal and parotid lymph glands. The nerves supplying the muscles 

 of the tympanic cavity have already been referred to (pp. 832, 834). The mucous membrane 

 receives its nerves from the tympanic plexus, which is described on p. 786. The chorda tympani 

 branch of the facial nerve passes from behind, upwards, and forwards through the tympanic 

 cavity. Its course is described on p. 782. 



Early Condition of Tympanic Cavity During the greater part of intra-uterine existence 

 the tympanic cavity is almost completely filled by a soft, reddish, jelly-like embryonic tissue 

 in which there is a slit-like space lined with epithelium. Towards the end of foetal life this tissue 

 disappears and at birth the cavity is filled with fluid which becomes absorbed, after the entrance 

 of air from the nasal part of the pharynx through the auditory tube. 



