268 



The Malleus 



AUDITORY BIOPHYSICS 



As the name implies, the malleus is a mallet-shaped bone. It has a 

 handle and an irregular pestle-shaped head. The head (capitulum) is 

 separated from the handle (manubrium) by a constriction, the neck 

 (collum), to which the tendon of the tympanic tensor is attached. 



Figure VI 1-7 shows the detailed construction of an average malleus, 

 as adopted by Stuhlman [1937] for a comprehensive study of the trans- 

 mission characteristics of the ossicle chain. 



Center of rotation 

 Malleus motion out 

 y 



Convex surface 



Concave 



inner 

 surfaces 



C. of rot. malleus 'lib 



Incus 



nferior parabolic arch 



Stapes 



Fig. VII-7. Details of structure and articulation of malleus, incus, and attached 

 stapes. To visualize their articulating positions, rotate malleus 180° to the right, 

 placing concave surfaces over convex surfaces of incus. (Stuhlman [1937].) 



The average mass of a malleus was found to be 23 mg. The average 

 overall distance from the end of its processus brevis to the end of the 

 manubrium or handle was about 5.8 mm. Its axis of rotation for small 

 angular displacements was taken as passing through its center of gravity 

 in the neck and continuing anteriorly through the anterior suspensory 

 ligament. The length of the manubrium lever arm was taken as 3 mm. 



The posterior surface of the head of the malleus possesses an 8-shaped 

 double-socket concave facet where it articulates with the incus in cor- 

 responding convex surfaces to form an interlocking " saddle-shaped 

 articulation." 



Tensor Tympani 



The tympanic tensor may be considered as pulling inward and func- 

 tioning as an equilibrator to govern the tension on the tympanic mem- 

 brane and on the suspensory and capsular ligaments. This tensor and 



