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 ene neonate 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, madleus or hammer, incus or anvil, and stapes or stirrup. The 
fourth, or orbicular, is by many considered a mere epiphysis to the i 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. ‘he head presents an articulation for the incus. 
Incus is placed internal and posterior to the malleus, and bears some 
resemblance to a bicuspid tooth; it presents a body or ned and a short and 
long crus. The body is less 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 orbiculare or lenticulare. 
The stapes, or stirrup, 1s 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 thin 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, chiefly lodged in the bony 
canal above the cochleariform process and Kustachian 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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