546 



ORGAN OF HEARING. 



be muscular by Sir Everard Home and others, 

 but this has not been confirmed by microscopi- 

 cal examination. 



Mr. Shrapnell* describes at the anterior and 

 superior part of the membrana tympani, above 

 the short process of the malleus and its suspen- 

 sory ligament, and where the groove in the bone 

 is deficient, a flaccid tissue, composed of irre- 

 gularly arranged fibres, to which he gives the 

 nameof membrana flaccida, in opposition to the 

 rest of the membrana tympani, which he calls 

 iiicniliriiiiu tensti. This flaccid tissue is more 

 developed in some of the lower animals, the 

 sheep and hare for instance, than in man, and 

 can be readily made to bulge out towards the 

 auditory passage by blowing air into the Eusta- 

 chian tube. But we cannot look upon it, with 

 Mr. Shrapnell, as properly forming any part of 

 the membrana tympani. It is merely a mass 

 of dense, reddish, vascular cellular tissue, sur- 

 rounding the neck of the malleus, and conti- 

 nuous with a similar tissue found under the 

 lining integument of the upper wall of the 

 osseous auditory passage. It is this same tis- 

 sue which has been described as a muscle, and 

 sometimes as a ligament. 



The membrana tympani has been said to 



rsent in the natural state a perforation closed 

 _ a valve. Rivinus,f though not the first to 

 mention it, dwelt on it, however, in a parti- 

 cular manner, hence the perforation has been 

 called hiatus Rivininnus. The subject has been 

 more recently taken up by Wittmann and 

 Vest.J 



The membrana tympani receives a nerve 

 from the third division of the fifth, which has 

 communications with filaments of the chorda 

 tympani. 



To resume our description of the cavity of 

 the tympanum: In the upper wall of the 

 tympanum there is an excavation for receiving 

 the upper part of the incus, and leading from 

 that, at the upper and back part of the tympa- 

 num, is a short, wide, triangular canal, with a 

 rough cellular surface. This is the passage to 

 the mastoid cells, through the medium of a 

 large cell, sinuositas mastoidca s. sinus manniiil- 

 luris, s. antrum mammillare, which already ex- 

 ists in the young bone between the squamous 

 and petrous portions. 



The mastoid cells are cavities in the mas- 

 toid process, all communicating with each 

 other. They are quite irregular in regard to 

 size, number, and relative situation. In early 

 life, as the mastoid process is not fully formed, 

 they do not exist, they are only found com- 

 pletely developed in the adult. 



Inferiorly, the cavity of the tympanum forms 

 a sort of furrow, which presents nothing parti- 

 cular. It is bounded by the plate of bone 

 which forms the outer wall of the jugular fossa. 



* On the form and structure of the membrana 

 tympani, in London Medical Gazette, vol. x. p. 

 120. London, 1832. 



t DC auditus vitiis, Lipsize, 1717, 4, p. 32. Tab. 

 adj. Fig. 1,6. c.t fig. 2, 6. 



} Ueber din Wittmannsche Trommelfellklappe, 

 in den medi/iiiisch. Jahrbiichern des oestr. Staates. 

 lid. v. Wien, 1819, p. 123, 133. 



Anteriorly, the cavity of the tympanum 

 opens into the osseous portion of the Eustuchiau 

 tube. 



The ossicles or small bones of the ear (ossi- 

 cula auditus s. uurium, Fr. osselets <te /' uuie ; 

 Germ.dieGehvrkriuclielchen,orGeh<>rbeinc/itn). 

 In the upper part of the cavity of the tympa- 

 num, there are three small bones articulated 

 with each other, and forming a chain which 

 reaches from the membrana tympani to the ves- 

 tibular fenestra. The bones are named malleus, 

 incus, and stapes, from their resembling more or 

 less respectively a hammer, an anvil, and a 

 stirrup iron. 



The innermost and most essential is the sta- 

 pes ; it is it alone which in birds and reptiles 

 remains, when the others have disappeared, or 

 been reduced to merely cartilaginous pieces. 

 The stapes is engaged in the vestibular fenes- 

 tra. 



The outermost of the chain, the malleus, is 

 in connexion with the membrana tympani. 



The hammer bone, (malleus,) Fr. le martcau, 

 Germ, das Hammer, presents a head, a neck, a 

 handle, and two processes, one longer, and one 

 shorter. 



The head, caput s. capitulum, is round and 

 smooth on one surface, and on the other pre- 

 sents a saddle-shaped depression, surrounded 

 by a small elevated border. The depression 

 articulates with the incus, and the border is for 

 the attachment of the synovial capsule of this 

 minute joint. 



The neck, collum s. cervix, is flattened in one 

 diameter, and joins the handle at an obtuse 

 angle. 



The handle, manubrium mallei, compressed 

 from the side corresponding to the articular 

 depression to the opposite side, and diminish- 

 ing in thickness towards its extremity, forms, 

 together with the short process, a double curve, 

 like an Italic f. The extremity is also com- 

 pressed, as if beaten flat, but in an opposite di- 

 rection, so that the broad surfaces of the extre- 

 mity correspond to the edges of the rest of the 

 handle. 



Short or blunt process, proccssus brevis s. 

 obtusus. From the projecting side of the an- 

 gle formed by the junction of the neck and 

 manubrium, this process, which is short, thick 

 and conical, rises. 



The long or slender process, processus longns, 

 s. gracilis, s. sp'mosus, s. Volii, springs from the 

 neck, and from that side of it which corres- 

 ponds with the non-articular surface of the 

 head. The long process is of considera- 

 ble length, and terminates in a broad, fiat, 

 spatula-like extremity, first described by Ilau,* 

 although the commencement or root of the 

 process itself had been previously delineated 

 and described by Folius. The long process is 

 generally found broken off, either from its being 

 so slender, or from its having been, especially 

 in old subjects, united to the groove in which it 

 is lodged. 



The anvil bone, incus, Fr. I'cnclume, Germ. 



* Boerhaave Prslect. in Insult., Prop. iv. p. 

 358. 



