Chap, iv.] 



HEARING. 



985 



to what in the dried skull appear as two foramina, but in the 

 fresh state are two membranous fenestras. One of these, oval 

 in shape, called the fenestra ovalis (Figs. 166, 170, 171 /.o.), lies 

 between the tympanic cavity on the outside and that part of 

 the perilymph space which surrounds the division of the mem- 



Fig. 170. Frontal (transverse vertical) section through the 

 Tympanum. (Left Ear.) (Schwalbe.) 



The figure, partly diagrammatic, is magnified twice, and shews the front part 

 of the tympanum as seen from behind ; the incus has been removed, the artic- 

 ular surface on the head of the malleus being indicated. 



mt. The membrana tympani. mf. membrana flaccida. mbr. handle of the 

 malleus, p.b. short process of the malleus. 



Ig.e. external ligament, Ig.s. the superior ligament of the malleus. 



TT. The bony projection from which the tendon of the tensor tympani 

 passes to the malleus, f.o. the fenestra ovalis. v. the front part of the vesti- 

 bule, c. the beginning of the first (basal) turn of the cochlea. 



Fig. 171. Diagram of the median Wall of the Tympanum of the Left 

 Ear. Magnified twice. (After Schwalbe.) 



1. The tympanic, 2. the epitympanic region ; below the reference figure is 

 seen the gentle prominence due to the ampullae. A. the antrum mastoideum, the 

 line ee marking its limits. E.t. the Eustachian tube. T. T. the groove for the 

 tensor tympani. f.o. the depression of the fenestra ovalis, the fenestra itself 

 being shaded, f.r. the depression leading to the fenestra rotunda ; above, and 

 obliquely to the left of this, lies the projection caused by the base of the cochlea. 

 St. the prominence for the stapedius, with the orifice for the exit of the tendon. 

 VII. the course of the facial nerve. The tympanum proper lies within the let- 

 ters a. b. d.e. 



