ORGAN OF HEARING. 



546 



process. The muscle of the malleus receives 

 a nervous branch from the otic ganglion. 



By the action of this muscle, the handle of 

 the malleus is drawn inwards and forwards, 

 whilst the head is moved in the opposite direc- 

 tion, in consequence of the bone moving on its 

 long process as on an axis. The result of this 

 movement of the bone is, that the membrana 

 tympani, which is attached to the handle of the 

 malleus in its whole length, is also drawn in- 

 wards and stretched. Besides the tension to 

 which the membrana tympani is thus subjected, 

 the base of the stapes is forced against the ves- 

 tibular fenestra, in consequence of the move- 

 ment communicated by the head of the malleus 

 to the incus, which tends to press inwards the 

 long extremity of the latter. 



Muscle of the stapes, M. stapedius. This is 

 lodged, and takes origin in the cavity of 

 the pyramid already described. Much paler 

 and smaller than the preceding muscle, it is 

 inserted into the posterior and upper part of the 

 head of the stapes by a slender tendon, which 

 issues by the aperture in the summit of the py- 

 ramid, and proceeds downwards and forwards 

 to its termination. 



The stapedius muscle receives a nervous fila- 

 ment from the facial nerve. 



The first effect of the action of this muscle 

 will be to press the posterior part of the base of 

 the stapes against the vestibular fenestra. At 

 the same time the long branch of the incus will 

 be drawn backwards and inwards, and the head 

 of the malleus being, by this movement of the 

 incus, pressed forwards and outwards, its han- 

 dle will be i a-ried inwards, and the membrana 

 tympani thus put on the stretch. Breschet 

 calls the muscle of the stapes a laxator, but I 

 do not know on what grounds. 



Magendie* mentions the circumstance that 

 in the stapedius muscle of the ox and horse, 

 there is imbedded a small lenticular bone. 

 Professor Berthold of Gottingenf has more 

 lately called attention to the same circumstance. 

 Berthold has not found this bone in man, nor 

 sheep, nor deer, nor goats, nor swine. In the 

 ox and calf it is about one-half to three-fourths 

 of a line in its longest diameter, and one-third 

 in the shortest, and lies surrounded by the mus- 

 cular and tendinous substance where the for- 

 mer passes into the latter. In the horse it is a 

 little nearer the lower margin of the muscle and 

 tendon, and is much smaller than in the ox; 

 moreover, it is not round, but is a longish plate, 

 somewhat thicker in the middle. 



At the place where the stapedius muscle is 

 inserted into the stapes, HyrtlJ has sometimes 

 found in the human ear a small process of bone 

 which in some cases was so long as to extend 



* Sur les organes qui tendent ou relachent la mem- 

 brane du tympan et la cbaine des osselets de 1'ouie 

 dans 1'homme et les aniinaux mammiieres. In 

 Journal de Physiologie experimentale, t. 1., p. 

 346. Paris, 1821. 



t Ueber ein linsenformiges Knochelchen im 

 Musculus Stapedius mehrerer Saugethiere. In 

 Mueller's Archiv. Jahrg. 1838. 



$ Beitr'age zur patbologiscben Anatomie des 

 Gehbrorgans, in the Medicin. Jabrbiicher des 

 k. k. oesti. Staates. Wien 1836. Bd. xx. p. 

 439. 



into the belly of the muscle itself. Teichmeyer* 

 has described this free bone of the stapedius 

 muscle as constant in man. 



Having described the walls and contents of 

 the cavity of the tympanum, we come now to 

 speak of the membrane which lines it. 



The lining membrane of' the cavity of the 

 tympanum is in continuity with the mucous 

 membrane of the throat, through the F.ustachian 

 tube. Extremely delicate, and in some parts 

 very vascular, it is not merely a mucous 

 membrane, but is theoretically a combination 

 of periosteum and mucous membrane, being 

 what Bichat called fibro-mucous. Itin vests all 

 the elevations and depressions observed on the 

 walls of the tympanum, and extends into the 

 mastoid cells. The outer layer of the mem- 

 brane of the fenestra rotunda, membrana tym- 

 pani secunduriti, is a continuation of it. 



The base of the stapes is fixed by its circum- 

 ference to the outer edge of the groove, which 

 encircles the vestibular fenestra, by a membrane 

 or ligament. The lining membrane of the ves- 

 tibule, continued over the base of the stapes 

 from within, also invests the inner surface of 

 this annular ligament, whilst the outer surface 

 of it is covered by the membrane lining the 

 tympanum as it is reflected on the stapes. 



The membrane lining the tympanum invests 

 the small bones and the tendons of their mus- 

 cles where they run free in the cavity. A fold 

 of it tills up the space bounded by the crura and 

 base of the stapes. The chorda tympani, also, 

 in its passage across the tympanum, is enve- 

 loped by it. Lastly, it forms the inner bor- 

 rowed layer of the membrana tympani, cover- 

 ing and adhering closely to the handle of the 

 malleus. 



The Eustachian tube, (tuba Euntachii, s. ca- 

 nalis palatinus tympani; Fr. la trompe d'Eus- 

 tachi ; Germ, die Eustuchische Rohre oder dtr 

 Gaumeiigang des mittkren Ohrs.) The 

 Eustachian lube is a passage of communication 

 betwixt the cavity of the tympanum and the 

 throat. In length about an inch and a half, it 

 is directed from behind forwards, from without 

 inwards, and from above downwards. Its gut- 

 tural orifice is wider than that by which it opens 

 into the tympanum. 



Proceeding from the tympanum, its first part 

 is an osseous canal, the osseous part of the Eus- 

 tachian tube; the walls of the remainder of it 

 are composed partly of cartilage, partly of 

 fibrous membrane, the cartilaginous and mem- 

 braneous portion of the Eustachian tube. 



The osseous part of the Eustachian tube, pars 

 ossea tuba Eustachii, begins at the anterior and 

 lower part of the tympanum, by a funnel-like 

 orifice, and runs forwards and inwards on the 

 outside of the carotid canal, and below that for 

 the reception of the internal muscle of the mal- 

 leus. It is about half an inch in length, and 

 ends by a notched and irregular edge at the re- 

 entering angle, between the squamous and 

 petrous portions of the temporal bone. Its 

 calibre contracts in its course forwards, and is 

 compressed from without and below inwards 



* Vindiciae quorundam inventorum anat. in liubium 

 vocatorum. Jeiiae. 1727. 4. 



