Royal Society. 425 
under the bafis of the Concha^ and inclofes the head of the 
Malleus^ and almoft the whole Incus ; the third cavity, which 
is the largellof all, regards the internal orifice of the aquieduct, 
and contains in it a portion of the belly of the firft muicle of the 
internal ear, and of the Incus-t together with both its Apophyfes^ 
and alfo indoles the Stapes^ Os letnkulare^ the tendon of the 
fecond mofcle of the internal ear, together w'th tiie neck, and 
handle of the Malleus : In fine this membrane, is formed in fome 
ftibjef^s in fuch a manner, as that a fmall portion of it becomes a 
very (lender little membrane like a partition wall, which equally 
divides the fpace comprehended by the third and greatefl cavity 5 
this little membrane has not been defcribed by any anatomift, io 
far as Vieujjens could learn, as rarely occuring, and where it is 
found, it adheres to the fuperior part of the bafis of the Concha^ 
and by its inferior to the external membrane of the T'ympanum^ 
which clofes up the extremity of the Meatus Auditorius^ and 
feems to imerle^t it tranfverfely into almofl two equal parts, as 
far as the extremity of the handle of the Malleus^ to which it 
adheres^ nay and a little farther 5 fo that this little membrane, 
together with the extremity of the handle of the Malleus^ draws 
the middle part ofthe external membrane of the Tj'w/^^w/^ towards 
the internal parts of its cavity, and gives it fuch an inclination as to 
be a little concave towards the Meatus Auditorius^ and a little con- 
vex towards the cavity of the Tympanum 5 this little membrane, 
in lubjedls where it is found, is apt to hinder the exterior mem- 
brane of the Tympanum from being ftretched too much by the 
violent contra6lions of the monogaflric mufcle of the internal ear, 
or from being torn by the extremity of the handle of the Malleus ^ 
when the above mentioned muicle is aflTe^ted with any convul five 
motions; lb that the little membrane leems in fom,e meafure to 
iupply the office of an antagonifl to the monogaflric mufcle, if it 
be confidered as a6iing by its flender and longer tendon, as will 
afterwards appear; if any one would fatisfy his curiofity in this 
relpeft, let him feparate the Os Tetrofum from the reft of the 
fcullof a perfon that has been ftrangled ; or of one that has died 
of a phrenfy or apoplexy, after which it muft be laid up m a dry 
place for two days, that the membrane juft now mentioned may 
become fomewhat dry, and contracted, in order the better to le- 
parate it from the internal fuperficies of the cavity wherein h is 
contained, and to prevent its being torn; afterwards that very thin 
bone, which conilitutes the fuperior part of the Tympanum.^ 
muft be fkilfully cut away with a knife into fmall pieces ; which 
is no iboner done, than this membrane that before lay concealed 
Vol. III. H h h withia 
