2 3 8 



ELEMENTS OF MAMMALIAN ANATOMY. 



through the external auditory meatus. The more dor- 

 sal foramen is the fenestra ova Us, which in the recent 

 state is closed by a membrane to which the foot of the 

 stapes is attached. The ventral one is the fenestra 

 rotundum, also closed by a membrane in the recent 

 state. In the dry skull the fenestra ovalis opens into 

 the first or basal whorl of the cochlea, and the fenestra 



rotundum opens into the vesti- 

 bule of the internal ear. The 

 Eustachian tube (Fig. 18), whose 

 opening may be seen cephalad of 

 the auditory bulla, connects the 

 middle ear with the posterior 

 nares and thus admits air to the 

 tympanic cavity. 



To demonstrate further the 

 anatomy of the middle ear, one 

 should clean the flesh from a 

 fresh or preserved head and care- 

 fully cut away the ventral walls 

 of both chambers of the auditory 

 bulla (Fig. 17). 



In the middle ear are three 

 bones, the malleus, incus, and 

 stapes, commonly called ham- 

 mer, anvil, and stirrup. They 



form a crooked chain across the cavity. The long process 

 of the malleus is fastened throughout nearly its whole 

 length to the inner or mesal surface of the membrana 

 tympani, and its enlarged extremity articulates with the 

 body of the incus. The latter has two legs, to one of 

 which the stapes is attached. The base of the stapes is 

 inserted in the membrane closing the fenestra ovalis (Figs. 

 17 and 107). 



FIG. 107. DIAGRAM OF THE 

 MAMMALIAN EAR. 



The internal ear is repre- 

 sented removed about a 

 centimeter from the mid- 

 dle ear and slightly rotated 

 to the left. The base of the 

 stapes, s, in nature, covers 

 the fenestra ovalis, o-v; c, 

 basal whorl of the cochlea ; 

 ea, external auditory meat- 

 us ; e u, opening of the Eu- 

 stachian tube ; i, incus ; in , 

 malleus ; sc, semicircular 

 canals ; ve, vestibule ; /, 

 tympanum. 



