384 



SCIENCE. 



[Vol. I., No. 14. 



membrane.' Above the promontory, and over 

 the position of the round window, is a concave 

 recess, at the bottom of which is the oval 

 window.'^ This is half oval or slightly reni- 

 form, with its longer diameter nearlj' horizontal, 

 and it is directed outwardly. It communicates 

 with the vestibule, and, when complete, is 

 closed by the insertion of the base of the 

 stirrup. 



In advance of the oval window is the pro- 

 jecting end of the scroll or tube, which serves 

 as a receptacle for the tj'mpanic tensor muscle. 



Below the promontor3-, curving fore and aft 

 around it, is a concave, rough, cellular recess, 

 which extends outwardly, and is defined bj- the 

 t^-mpanic margin of the tj^mpanic plate. The 

 lower part of the recess is the floor of the tym- 

 panum, situated above the jugular fossa ; its 

 back part forms the lower portion of the pos- 

 terior wall of the tympanum ; and its fore part, 

 the lower portion of the anterior wall, situ- 

 ated just external to the ascending portion of 

 the carotid canal. Above the recess, in front 

 and inwardlj', is the orifice of the eustachian 

 tube. In front of this is the short, narrow, 

 oblique canal, which opens into the glenoid 

 fissure, and receives the long process of the 

 mallet, together with the tympanic cord. 



Within the posterior wall of the tympanum 

 is the descending portion of the facial canal ; 

 and in advance of this is the receptacle for the 

 stapedius muscle. The receptacle is a cylin- 

 droid cavity, about a fourth of an inch long. 

 Ascending in front of the facial canal, it then 

 curves forward beneath this, and tapers to an 

 aperture at the summit of a little conical 

 process, the pyramid. It is separated from 

 the facial canal bj'' a thin partition ; but this is 

 not unfrequently more or less imperfect, and 

 is then, in the recent state, closed b}' fibrous 

 membrane. The receptacle also communicates 

 with the facial canal by one or two small canals 

 for the passage of the vessels and nerve of the 

 stapedius. The pj^ramid projects forward into 

 the tj'mpanic atrium, behind the position of the 

 oval window. It is commonly- connected with 

 the contiguous wall b3^ several little radiating 

 bars, one of which joins the promontory. 

 Between the pj^'amid and the recesses of the 

 round and oval windows there are two vacant 

 recesses. 



Close to the back margin of the tympanic 

 orifice of the external auditory meatus, a little 

 below the level of the pyramid, is the opening 

 of a small canal from the facial canal, which 

 admits the tj'mpanic cord into the tymp.anum. 



The attic ^ of the tympanum is a pyramidal 

 recess over the atrium, and above the tj-mpanic 

 orifice of the external auditorj' meatus. Its 

 upper anterior boundary is the tegmen, which 

 separates it from the cranial cavit}', and is 

 mostlj' provided with a laj-er of spongy sub- 

 stance of variable thickness. Tts inner boun- 

 darjr is a convex prominence (fig. 1, e; fig 2, 

 b) produced by the contiguous portions of 

 the external semicircular and facial canals. 

 Its outer boundary is the wide crescentic tym- 

 panic scute (fig. 1, &; fig. 2, c) of the audi- 

 tory plate. It opens above the prominence 

 of its inner boundarj-, outward and backward, 

 bj' a large aperture - into the mastoid antrum. 

 Beneath, it opens into the atrium by an ellip- 

 tical aperture, formed internallj' by the ridge 

 of the facial canal, and -externally liy the 

 tympanic margin of the auditory plate. The 

 attic is partially occupied by the mallet and 

 anvil, which thence, bj^ the handle of the 

 former, and the long process of the latter, 

 extend into the atrium. 



The mastoid antrum (fig. 1, d; fig. 2, /) 

 is a prolongation of the attic backward and 



Fio. 2. — Section uftlie left temporal bone, through the fiquamosa, 

 immediately in advance of the external auditory meatus. 

 a, atrium of the tympanum ; 6, prommence on the inner back 

 part of the attic; c, scute at the outer part of the attic; (f, 

 auditory plate; e, tegmen; /, mastoid antrum; g, anterior 

 passage of the same; /i, canal for the long process of the mal- 

 let; i, hiatus of the facial canal; j, eustachian tube. 



outward in the spongy substance of the mas- 

 toidea. It is of variable size, ordinarily 

 ranging from that of the attic to double the 

 dimensions of this. It sometimes ends in a 

 blunt, flask-like recess, but is oftener more or 

 less extended downward among the cellules 

 of the mastoid process. Frequentlj' it gives 

 olf a smaller fork or passage (fig. 2, g), which 

 is directed outward and upward among the 



' Atticue tympanicus, upper chamber of the tympanum of 

 Huxley. 



2 Petro-raastoid canal of Sappey. 



