156 . ANTHROPOLOGY. 



is to admit external air into the tympanum, by means of which the mem- 

 brane is enabled to resist the pressure of the atmosphere ; it also serves to 

 conduct the secretions of the tympanic cavities into the fauces. 



The tympanum also presents another small opening or canal, anteriorly 

 and inferiorly, which leads to the inner side of the fissure of Glasser, and 

 transmits the chorda tympani nerve. The cavity of the tympanum is tra- 

 versed by a chain of small bones, one attached externally to the membrana 

 tympani, and another to the membrane in the fenestra ovalis. 



3. OssicULi OF THE Ear. The small bones of the ear are three, or 

 according to some, four in number, and are named from a fancied resem- 

 blance, malleus or hammer, incus or anvil, and stapes or stirrup. The 

 fourth, or orbicular^ is by many considered a mere epiphysis to the long leg 

 of the incus. 



Malleus is immediately within the membrana tympani, and connected to, 

 it ; it presents a head, neck, manubrium or handle, and long and short pro- 

 cesses. The head presents an articulation for the incus. 



IncijLs is placed internal and posterior to the malleus, and bears some 

 resemblance to a bicuspid tooth ; it presents a body or head, and a short and 

 long crus. The body is lodged in the recess of the tympanum, and receives 

 the head of the malleus in its deep concave surface. The short crus occupies 

 the opening into the mastoid cells. The long crus descends vertically in 

 the tympanum, parallel to the handle of the malleus. At its extremity is 

 the round tubercle, which is sometimes united to it like an epiphysis, and 

 at others separable from it, when it is called os orhicnlare or lenticulare. 



The stapes, or stirrup, is placed horizontally between the crus of the incus 

 or orbicular bone, and the fenestra ovalis, to the membrane of which its 

 base is attached. Its head presents a small cavity for articulation with the 

 orbicular bone, or with the crus of the incus; its base is a tliin plate, closing 

 the fenestra ovalis. 



The articulations between these three bones are furnished with synovial 

 membranes and capsular ligaments, and are further secured in their places 

 by three ligaments. One extends from the head of the malleus to the upper 

 wall of the tympanum ; another connects the short process of the incus 

 with the opening of the mastoid cells ; and a third extends from the margin 

 of the fenestra ovalis to the margin of the base of the stapes. 



4. Muscles of the Tympanum are only two in number, the stapedius 

 and the tensor tympani. The stapedius arises within the pyramid, and is 

 inserted into the back part of the neck of the stapes. The tensor tympani 

 is a very distinct and long fibro-muscular cord, chiefl}" lodged in the bony 

 canal above the cochleariform process and Eustachian tube. It arises from 

 the cartilage of that tube, and from the adjacent portion of the sphenoid 

 bone. It is inserted into the inner, anterior, and superior portion of the 

 handle of the malleus. The use of the stapedius muscle is not well ascer- 

 tained ; that of the tensor tympani is to draw the handle of the malleus 

 inwards and forwards, by which the membrane is rendered more tense. 

 Two other muscles, laxator major and minor as described by some authors, 

 appear to be only ligamentous fibres. 



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