1046 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 



A superior ligament of the incus (lig. incudis superius] has been described, but it 



is little more than a fold of mucous membrane. 



The vestibular surface and the circumference of the base of the stapes are covered 



with hyaline cartilage; that encircling the base is attached to the margin of the 



fenestra vestibuli by a fibrous ring, the annular 

 ligament of the base of the stapes (lig. annulare 

 baseos stapedis) . 



The Muscles of the Tympanic Cavity (musculi 

 ossiculorum auditus) are the Tensor tympani 

 and Stapedius. 



The Tensor tympani, the larger, is contained 

 in the bony canal above the osseous portion of 

 the auditory tube, from which it is separated 

 by the septum canalis musculotubarii. It 

 arises from the cartilaginous portion of the 

 auditory tube and the adjoining part of the 

 great wing of the sphenoid, as well as from the 

 osseous canal in which it is contained. Passing 

 backward through the canal, it ends in a slen- 

 der tendon which enters the tympanic cavity, 

 makes a sharp bend around the extremity of 

 the septum, and is inserted into the manubrium 

 of the malleus, near its root. It is supplied 

 by a branch of the mandibular nerve through 

 the otic ganglion. 



The Stapedius arises from the wall of a con- 

 ical cavity, hollowed out of the interior of the 

 pyramidal eminence; its tendon emerges from 



the orifice at the apex of the eminence, and, passing forward, is inserted into the 



posterior surface of the neck of the stapes. It is supplied by a branch of the facial 



nerve. 



Actions. The Tensor tympani draws the tympanic membrane medialward, and thus increases 

 its tension. The Stapedius pulls the head of the stapes backward and thus causes the base of 

 the bone to rotate on a vertical axis drawn through its own center; the back part of the base is 

 pressed inward toward the vestibule, while the forepart is withdrawn from it. By the action of 

 the muscle the tension of the fluid within the Internal ear is probably increased. 



The Mucous Membrane of the Tympanic Cavity is continuous with that of the pharynx, through 

 the auditory tube. It invests the auditory ossicles, and the muscles and nerves contained in 

 the tympanic cavity; forms the medial layer of the tympanic membrane, and the lateral layer 

 of the secondary tympanic membrane, and is reflected into the tympanic antrum and mastoid 

 cells, which it lines throughout. It forms several vascular folds, which extend from the walls 

 of the tympanic cavity of the ossicles; of these, one descends from the roof of the 

 cavity to the head of the malleus and upper margin of the body of the incus, a second 

 invests the Stapedius muscle: other folds invest the chorda tympani nerve and the Tensor 

 tympani muscle. These folds separate off pouch-like cavities, and give the interior of the tym- 

 panum a somewhat honey-combed appearance. One of these pouches, the pouch of Prussak, 

 is well-marked and lies between the neck of the malleus and the membrana flaccida. Two other 

 recesses may be mentioned: they are formed by the mucous membrane which envelops the 

 chorda tympani nerve and are situated, one in front of, and the other behind the manubrium of 

 the malleus; they are named the anterior and posterior recesses of Troltsch. In the tympanic 

 cavity this membrane is pale, thin, slightly vascular, and covered for the most part with colum- 

 nar ciliated epithelium, but over the pyramidal eminence, ossicles, and tympanic membrane 

 it possesses a flattened non-ciliated epithelium. In the tympanic antrum and mastoid cells 

 its epithelium is also non-ciliated. In the osseous portion of the auditory tube the membrane is 

 thin; but in the cartilaginous portion it is very thick, highly vascular, and provided with numerous 

 mucous glands; the epithelium which lines the tube is columnar and ciliated. 



Vessels and Nerves. The arteries are six in number. Two of them are larger than the others, 

 viz., the tympanic branch of the internal maxillary, which supplies the tympanic membrane; 





FIG. 919. Chain of ossicles and their liga- 

 ments, seen from the front in a vertical, trans- 

 verse section of the tympanum. (Testut.) 



