THE EAR, HEARING, TASTE AND SMELL 



229 



(the prominent bony mass just behind the ear) has many hollows 

 in it which communicate with the cavity of the middle ear and 

 may become infected from it. Infection of these hollows gives 

 rise to the extremely grave condition, mastoiditis. 



The Auditory Ossicles. Three small bones lie in the middle 

 ear forming a chain from the drum membrane to the oval fora- 

 men. The external bone (Fig. 70) is the malleus or hammer; the 

 middle one, the incus or anvil; and the internal, the stapes or 

 stirrup. The malleus, M, has an upper enlargement or head, 

 which carries on its inner side an articular surface for the incus; 

 below the head is a constriction, the neck, and below this two 

 processes complete the bone; one, the long or slender process, is 

 embedded in a ligament which reaches from it to the front wall of 

 the tympanic cavity; the other process, the handle, reaches down 

 between the mucous membrane lining the inside of the drum 

 membrane and the membrane proper, and is firmly attached to 

 the latter near its center and keeps the membrane dragged in 

 there so as to give it its peculiar 

 concave form, as seen from the 

 outside. The incus has a body 

 and two processes, and is much 

 like a molar tooth with two roots. 

 On its body is an articular hollow 

 to receive the head of the malleus; 

 its short process ( Jb) is attached by 

 ligament to the back wall of the 

 tympanum; the long process (Jl) 

 is directed inwards to the stapes; 

 on the tip of this process is a little 

 knob, which represents a bone (os 

 orbiculare) distinct in early life. 

 The stapes (S) is extremely like a 

 stirrup, and its base (the footpiece 

 of the stirrup) fits into the oval foramen, to the margin of which 

 its edge is united by a fibrous membrane, allowing of a little play 

 in and out. 



From the posterior side of the neck of the malleus a ligament 

 passes to the back wall of the middle ear: this, with the ligament 

 embedding the slender process and fixed to the front wall of the 



Mm 



FIG. 70. The auditory ossicles of 

 the right ear, seen from the front. M , 

 malleus; J, incus; S, stapes; Mcp, 

 head of the malleus; Me, neck of 

 ditto; Ml, long process; Mm, handlo; 

 Jc, body; Jb, short, and Jl, long 

 process of incus; Jpl, os orbiculare; 

 Scp, head of stapes. 



