TYMPANIC BONES. 



537 



Mcp 



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 imbedded in a 

 ligament which reaches from it to the front Avail of the 

 tympanum; 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 lat- 

 ter near its centre and 

 keeps the membrane 

 dragged in there so as to 

 give it its peculiar concave 

 form, as seen from the out- 

 side. The incus has a body 

 and two processes and is 

 much like a molar tooth 

 with two fangs. 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 tym- 

 panum; the long process 

 stapes; on the tip of this 



J P 1 



Mm 



FIG. 144. The auditory ossicles of the 

 right ear, seen from the front. M, mal- 

 leus; J, incus; 8, stapes: Mcp, head of 

 the malleus ; Me, neck of ditto ; Ml, long 

 process; Mm, handle: Jc,body, J6, short, 

 and Jl, long process, of incus; Jpl, o& 

 orbiculare: Scp, head of stapes. 



(Jl) is directed inwards to tha 

 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 foot- 

 piece of the stirrup) fits into the oval foramen, to the mar- 

 gin 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 tympanum: this, 

 with the ligament imbedding the slender process and fixed 

 to the front wall of the tympanum, forms an antero-pos- 

 terior 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. 144 

 just below the neck of the malleus and perpendicular to tha 



