820 



SPECIAL SENSES. 



by its smaller extremity with the long process of the incus. Its base is oval (0*, Fig. 

 259) and, with its annular ligament, is applied to the fenestra ovalis. The direction of 



the stapes is nearly at a right angle with the 

 long process of the incus in the natural state 

 (8, Fig. 260). 



There are three well-defined muscles con- 

 nected with the middle ear. Of these, two are 

 attached to the malleus, and one, to the stapes. 

 The largest of the three muscles is the tensor 

 tympani, called sometimes the internal muscle 

 of the malleus. Its fibres arise from the carti- 

 laginous portion of the Eustachian tube, the 

 spinous process of the sphenoid bone, and the 

 adjacent portion of the temporal. From this 

 origin, it passes backward, almost horizontally, 

 to the tympanic cavity. In front of the fenes- 

 tra ovalis, it turns, nearly at a right angle, over 

 'a bony process, and its tendon is inserted into 

 the handle of the malleus at its inner surface 

 near the root. The tendon is very delicate, 

 and the muscular portion is about half an inch 

 in length (10, Fig. 258). The muscle and its 

 tendon are enclosed in a distinct fibrous sheath. 

 The action of this muscle is to draw the handle 

 of the malleus inward, pressing the base of the 

 stapes against the membrane of the fenestra ovalis and producing tension of the mem- 

 brana tympani. The fibres of this, and of all the muscles of the middle ear, are of the 

 striated variety. The tensor tympani is supplied with motor filaments from the otic 

 ganglion, which are probably derived from the facial nerve. 



FIG. 259. Ossicles of the tympanum of the right 

 side ; magnified 2 diameters. (Arnold.) 



A, malleus; 1, its head; 2, the handle; 3, long, or 

 slonder process ; 4, short process ; B, incus ; 1, its 

 body ; 2, the long process with the orbicular pro- 

 cess; 3, short, or posterior process; 4, articular 

 surface receiving the head of the malleus ; <J, 

 stapes; 1, head; 2, posterior crus; 3. anterior 

 crus ; 4, base ; C*. base of the stapes ; D, the three 

 bones in their natural connection aa seen from the 

 outside ; a, malleus ; 6, incus ; c, stapes. 



FIG. 260. The right temporal lone, the petrosal portion removed, showing the ossicles seen from within. From 



a photograph. (Kiidinger.) 



4, the incus, the short process of which is directed nearly in an horizontal direction backward ; 5, the long process of the 



incus, free in the tympanic cavity, articulated with the stapes; 6, the malleus, articulated with the incus; 7, the 



long process of the malleus in the Glasserian fissure ; 8. the stapes, articulated with the incus. This is drawn 



somewhat outward ; otherwise, the base of the stapes alone would be visible. This figure shows the handle of 



* the malleus attached to the membrana tympani. 



The laxator tympani, the external muscle of the malleus, arises from the spinous pro- 

 cess of the sphenoid bone and, by a few filaments, from the cartilaginous portion of the 



