THE MIDDLE EAR. 



733 



cavity. The tympanic cavity also presents an opening leading to the Eusta- 

 chian tube, and a small foramen which gives passage to the tendon of the 

 stapedius muscle. The Eustachian tube extends from the upper part of the 

 pharynx to the tympanum. 



The small bones of the ear are three in number ; the malleus, the incus> 

 and the stapes, forming a chain and connected together by ligaments (D. Fig. 

 264). These bones are situated in the upper part of the tympanic cavity. The 

 handle of the malleus (A, 2, Fig. 264) is closely attached to the membrana 

 tympani, and the long process (A, 3, Fig. 264) is attached to the Glasserian 

 fissure of the temporal bone. The malleus is articulated with the incus. The 

 incus (B, Fig. 264) is connected with the posterior wall of the tympanic cav- 

 ity, near the openings of the mastoid cells. It is articulated with the malleus, 

 and by the extremity of its long process (B, 2, Fig. 264), with the stapes. 

 The stapes (C, Fig. 264) is the most internal bone of the middle ear. It is 

 articulated by its smaller extremity with the long process of the incus. Its 

 base is oval (C', Fig. 264) 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. 265). Some anato- 

 mists describe a fourth bone as existing between the long process of the incus 

 and the stapes, but this is seldom dis- 

 tinct, usually being united either with 

 the incus or with the stapes. 



There are two well defined muscles 

 connected with the ossicles of the mid- 

 dle ear. One of these is attached to the 

 malleus, and the other, to the stapes. 

 The so-called laxator tympani probably 

 is not composed of muscular fibres and 

 should not be enumerated with the mus- 

 cles of the tympanum. 



The larger of the two muscles is the 

 tensor tympani. Its fibres arise from 

 the cartilaginous portion of the Eusta- 

 chian 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 

 fenestra ovalis it turns nearly at a right 

 angle over a bony process, and its ten- 

 don 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 (12*7 mm.) in length (10, Fig. 263). The muscle arid 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 membrana 



48 



FIG. 264. Ossicles of the tympanum of the right 

 side ; magnified 2 diameters (Arnold). 



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

 or slender process ; 4, short process ; B, in- 

 cus ; 1, its body ; 2, the long process, with the 

 orbicular process ; 3. short, or posterior pro- 

 cess ; 4, articular surf ace, receiving the head 

 of the malleus ; C, stapes ; 1, head ; 2, pos- 

 terior crus ; 3, anterior crus ; 4, base ; C'. 

 base of the stapes; D, the three bones in their 

 natural connection, as seen from the outside; 

 A, malleus ; B, incus ; C, stapes. 



