878 ORGAXS OF SPECIAL SENSE 



Some of the fil)re.s of this ligament have been descriljed as musevilar under the 

 name of the laxator tynipani muscle. But although occasionally nuiscular fibres 

 can be detected, in the majority of cases they appear to be absent. 



The external ligament of the malleus prevents the handle of the malleus 

 being turned too much outwards. It passes from the margins of the notcli of Ri- 

 vinus to the short process of the malleus. 



The ligament of the incus. — The short crus of the incus is covered Avith a layer 

 of fibro-cartilage and rests on a depression of the posterior tymi)anic Avail, close 

 to the oritice leading into the mastoid cells. The posterior ligament l)inds the 

 process to this Avall. 



The Muscles of the Tympanum. — Two muscles — the tensor tympani and the 

 stajjedius, Ijoth of which lie "within bony canals — transmit their tendons into the 

 cavity of the tympanum for insertion into the chain of ossicles. 



The tensor tympani is a penniform muscle about half an inch in length; it 

 arises in small part from the cartilaginous Eustachian tube and adjacent surface of 

 the sphenoid l)one as well as from the Avail of the canal in Avhich it lies. The 

 tendon, Avhich extends outAvards almost at a right angle to the belly of the muscle, 

 can 1)6 traced some distance iuAvards on its loAver aspect. It is inserted on the 

 inner margin of the handle of the malleus, near its root. The tendon glides 

 Avithin a sheath continuous Avith the periosteum lining the canal and surrounded 

 by mucous membrane. This muscle draAvs the handle of the malleus, and Avith it 

 the membrana tympani, iuAvards. 



The stapedius is a pyriform muscle; it arises from the interior of the 

 pyramidal eminence Avhich projects from the posterior Avail of the tympanum. 

 The tendon, Avhich can he traced iuAvai-ds for more than half the length of the 

 muscle, passes through the aperture at the summit of the eminence, to be inserted 

 into the posterior aspect of the neck of the stapes. Its tendon, like that of the 

 tensor tympani, is surrounded b}'' a fibrous sheath enveloped in the tympanic 

 mucous membrane. This muscle depresses the posterior, Avhilst at the same time 

 it slightly raises the anterior, end of the footpiece of the stapes. 



Nerves. — The stapedius is supplied by the facial nerve. The tensor tympani 

 receives a filament from the otic ganglion Avhich is probably derived from the 

 motor portion of the fifth nerve. 



The Mucous Membrane of the Tympanum is continuous through the Eusta- 

 chian tube with that Avliich lines the pharynx. It is thin and transparent, and in 

 places it is easily detached. 



Several vascular folds extend from the tympanic Avails to the ossicles, all of 

 Avhich receive a complete coA'cring of mucous membrane. 



The folds divide parts of the cavity into pouch-like recesses, four of Avhich, 

 lying in relation Avith the malleus, are of some importance; they are the superior 

 and inferior external pouches and the anterior and posterior pouches of Troltsch. 

 The superior external pouch lies in the epitympanic region, to the outer side of 

 the heads of the malleus and incus, and above the anterior and external ligaments 

 of the malleus, Avhich separate it from the inferior external pouch beloAV. The 

 inferior external pouch lies betAveen the last mentioned ligaments above and the 

 short process of the malleus beloAV. It is of special clinical importance because it 

 is bounded externally by the flaccid portion of the membrana tympani, anteriorly 

 it is closed but posteriorly it opens into the general cavity. The pouches of 

 Troltsch lie in front of and behind the handle of the malleus, and they are sepa- 

 rated by a fold of mucous membrane Avhich envelops the chorda tympani nerve. 



The mucous membrane of the roof of the tympanum and that Avhich lines 

 the meml)rana tympani and covers the ossicles ])ossesscs a flattened non-ciliated 

 epithelium. ElscAvhere for the most part, including the Eustachian tube, it is 

 columnar and ciliated. 



Vessels and nerves of the tympanum. — Arteries. — The tympanic branch 

 of tile internal maxillary Avhich passes through the Glaserian fissure, and the stylo- 

 mastoid branch of the posterior auricular Avhich passes through the Falloi)ian 

 canal, supply the front and back part of the tympanic cavity, and form a 

 vascular chain around the circumference of the membrana tympani. In addition 

 to these chief branches the hiatus Fallopii transmits the petrosal branch from the 



