638 THE EAR. 



The tensor tympani (musculus internus mallei) (fig. 449, 7), is the 

 largest of these muscles. It consists of a tapering fleshy part, about 

 half an inch in length, and a slender tendon. The muscular fibres arise 

 from the cartilaginous end of the Eustachian tube and the adjoining 

 surface of the sphenoid bone, and from the sides of the upper compart- 

 ment of the Eustachian orifice. In this canal the muscle is conducted 

 nearly horizontally backwards to the cavity of the tympanum. Imme- 

 diately in front of the fenestra ovalis the tendon of the muscle bends at 

 nearly a right angle over the end of the processus cochleariformis as 

 round a pulley, and, contained in a fibrous sheath, passes outwards, 

 to be inserted into the inner part of the handle of the malleus, close 

 to its root. 



The laxcdor fipnpani {laxator fympani major, Sommerring) is generally 

 believed to be distinctly muscular, but being partly concealed by a band 

 of fibrous tissue, doubts are still entertained by some observers as to 

 whether the structure known under this name is of a muscular or 

 lio-amentous nature. Arising from the spinous process of the sphenoid 

 bone, and slightly from the cartilaginous part of the Eustachian tube, 

 it is directed backwards, passes through the Glaserian fissure, and is 

 inserted into the neck of the malleus, just above the root of the pro- 

 cessus gracilis. 



The laxator tympani minor of Sommemng {posterior Ugamrnt of the malleus, 

 Lincke) is made up of reddish fibres, which are iixed at one end to the upper and 

 back part of the external auditory meatus, pass forwards and inwards between 

 the middle and inner layers of the membrana tympani, and are inserted into the 

 outer border of the handle of the malleus, and the short process near it (Som- 

 memng, Iconee Organi Auditus Humani, 1801). 



The sfapedkis is a very distinct muscle, but is hid within the bone, 

 beino- lodged in the descending part of the aqueductus Fallopii and in 

 the hollow of the pyramid. The tendon issues from the aperture at 

 the apex of that little elevation, and passing forwards, surrounded by a 

 fibrous sheath, is inserted into the neck of the stapes posteriorly, close 

 to the articulation of that bone with the lenticular process of the 



incus. 



A very slender spine of bone has been found occasionally in the tendon of the 

 stapedius in man : and a similar piece of bone, though of a rounder shape, exists 

 constantly in the horse, the ox, and other animals. This circumstance is the 

 more interesting in connection -n-ith the fact that cartilage occupies the position 

 of the stapedius before the muscle is developed. 



Fig. 450. — Outline of the Three Small Bones op 

 THE Left Ear as seen from before. Twice the 



NATURAL SIZE. 



This figure is designed to illustrate the effect of the 

 action of the tensor and laxator muscles of the tjrm- 

 panic membrane in connection with their relation to 

 the axis of rotation of the malleus. «, a', the malleus, 

 h, the incus seen behind it ; c, the stapes ; m, m', the 

 inner part of the meatus externus closed by the tym- 

 panic membrane ; g, processus gracilis ; the line t, in- 

 dicates the direction and position of the tendon of the 

 tensor tympani pulling the lower part of the malleus 



inwards, the line I, that of the laxator tympani pulling inwards the upper half of the 



malleus so as to force the handle outwards. 



Actions. — The malleus and incus move together round an axis extending back- 

 wards from the attachment of the processus gracilis of the malleus in the Glase- 



