THE EAR AND HEARING. 559 



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 centre and keeps Mcp 



the membrane dragged in there 



so as to give it its peculiar MC 



concave form, as seen from 



the outside. The incus has a MI^ 



body and two processes, and is 4 



much like a molar tooth with ~f~ 



two fangs. On its body is an 



articular hollow to receive the Mm 



head of the malleus; its short FlG i63.-The auditory ossicles of the 

 vvnr>pc<3 ( 77) \ io tiffnnliorl Kirlirra right ear. seen from the front. M, mal- 



piocess (Jo) is attached byiiga- le * s . j incus . s stapes . Mcp ^ head of 



mpnf fn HIP hoV \vnll nf flip the malleus ; Me, neck of ditto; Af J, long 



ment to tne Dack wall oi tne process . ^nl, handle ; jc, body,X short, 

 tympanum; the long process and <n< long process of incus; jpi, os 



* r orbiculare ; Scp, head ot stapes. 



(J7) is directed inwards to the 



stapes; on the tip of this process is a little knob, which rep- 

 resents a bone (05 orbiculare) distinct in early life. The 

 stapes (S) is extremely like a stirrup, and its base (the foot- 

 piece 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 liga- 

 ment passes to the back wall of the tympanum : this, with 

 the ligament imbedding the slender process and fixed to the 

 iront wall of the tympanum, forms an antero-posterior axial 

 ligament, on which the malleus can slightly rotate, so that the 

 handle can be pushed in and the head out and vice versa. 

 If a pin be driven through Fig. 163 just below the neck of 

 the malleus and perpendicular to the paper it will very fairly 

 represent this axis of rotation. Connected with the malleus 

 is a tiny muscle, called the tensor tympani; it is inserted on 

 the handle of the bone below the axis of rotation, and when 

 it contracts pulls the handle in and tightens the drum mem- 

 brane. Another muscle (the stapedius] is inserted into the 

 outer end of the stapes, and when it contracts fixes the bone 

 so as to limit its range of movement in and out of the fenestra 

 ovalis. 



The Internal Ear. The labyrinth consists primarily of 

 chambers and tubes hollowed out in the temporal bone and 



