674 



DISSECTION OF THE EAR. 



INNER VIEW OF THE MEM- 

 BRANA TYMPANI IN THE 



Fff.TUS, WITH THE MAL- 

 LKUS ATTACHED. 



a. Membrane or drum of 



the tympanum, 

 i. Malleus. 



c. Band of circular fibres 



at the circumference. 



d. Inferior, and e, superior 



tympanic artery. 

 / Tympanic bone. 



Fig. 240. of union of the squamous and petrous portions, out- 



side the passage for the carotid artery. Externally 

 it ends in a dilated and somewhat oval opening, with 

 an irregular margin, which gives attachment to the 

 cartilage. 



The cartilaginous part of the tube is nearly an 

 inch in length, and extends from the temporal bone 

 to the interior of the pharynx (p. 126). 



Through this tube the mucous membrane of the 

 drum of the ear is continuous with that of the pha- 

 rynx ; and through it the mucus escapes. 



The secondary membrane of the tympanum is 

 placed within the fenestra rotunda, and is rather 

 concave towards the tympanum, but convex towards 

 the cochlear passage, which it closes. 



It is formed of three strata, like the membrane on 

 the opposite side of the cavity, viz., an external or 

 mucous, derived from the lining of the tympanum ; 

 an internal or serous, continuous with that clothing 

 the cochlea ; and a central layer of fibrous tissue. 



OSSICLES OF THE TYMPANUM (fig. 242). Three 

 in number, they are placed in a line across the tym- 

 panic cavity. The outer one is named malleus from its resemblance to a 

 mallet ; the next, incus, from its similitude to an anvil ; and the last, 

 stapes, from its likeness to a stirrup. For their examination the student 

 should be provided with some separate ossicles. 



The malleus (fig. 241) is the longest bone, and is twisted and bent. It 

 is large at one end (a) (head) and small and pointed at the other (e) 

 (handle) ; and it has two processes with a narrowed part or neck. The 

 head or capitulum (a) is free in the cavity, is oval in shape, and is smooth 

 except at the back, where there is a depression for articulation with the 

 next bone. The neck (b) is the slightly twisted part between the head 

 and the processes. The handle or manubrium (e) decreases in size towards 

 the tip, and is flattened from before backwards ; but at the extremity it is 

 compressed from within outwards : to its outer margin the special fibrous 

 stratum of the membrana tympani is connected. 



The processes of the bone are two in number, long and short. The 

 short one (e) springs from the root of the handle on the outer side, and 

 touches the membrane of the tympanum. The long process processus 

 gracilis (c?), is a flattened slender piece of bone, which projects from the 

 neck of the malleus at the anterior aspect, and extends into the Glaserian 

 fissure : in the adult this process is joined with the surrounding bone, and 

 cannot be separated from it. 



The incus is a flattened bone (fig. 241), and possesses a body and two 

 processes. The body (b) is hollowed at the upper and anterior part to 

 articulate with the malleus. The two processes (short and long) extend 

 from the side opposite to the articulation : The shorter process (c) is 

 somewhat conical, and is received into the large aperture of the mastoid 

 cells : the long process (rf) decreases towards the extremity, where it curves, 

 and ends in a rounded point (e), the orbicular process. 



The stapes (fig. 241) has a base or wider part, and a head, with two 

 sides or crura, like a stirrup. The base (c?) is formed by a thin osseous 



