OssK'LKS OF THE TYMPANUM. 



809 



lining of the tympanum ; an internal, continuous with that lining of three 

 the cochlea ; and a central layer of fibrous tissue. 



OSSICLES OF THE TYMPANUM (figs. 298 and 299, p. 811). Three Ossicles of 

 in number, they are placed in a line across the tympanic cavity. m r m a re pa 

 The outer one is named malleus from its resemblance to a mallet ; three. 

 the next, incus, being compared 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. 298) is the longest bone, and is twisted and Malleus has 

 bent. It is large at the upper part (head ; a) and small and 

 pointed below (handle ; c) ; and it has two processes, with a 

 narrowed part or neck. The head or capitulum (a) is free in the head, 

 cavity, is club-shaped, and at the back has a depression for articula- 

 tion with the next bone. The mck (6) is the constricted part neck > 

 between the head and the processes. The handle or manubrium (c) handle, 



FIG. 298. THE THREE TYMPANIC OSSICLES OF THE RIGHT SIDE : THE CENTRAL 

 BONE is THE MALLEUS, THE LEFT-HAND ONE THE INCUS, AND THE RIGHT- 

 HAND ONE THE STAPES. 



Incus : 



a. Articular surface 

 for malleus. 



b. Body. 



c. Short process. 



d. Long process. 



e. Orbicular process. 



Malleus : 

 a. Head. 

 6. Neck, 

 c.. Handle. 



d. Long, and 



e. Short process. 



Stapes : 



a. Head. 



b. Neck. 



c. Anterior crus. 



d. Base. 



decreases in size towards the tip, and is compressed from before 

 backwards ; but at the extremity it is flattened from within out- 

 wards : to its outer margin the special fibrous stratum of the 

 membrana tympani is connected. 



The short process (e) springs from the root of the handle on the short 

 outer side, and is attached to the upper border of the tympanic 

 membrane where it bridges across the notch of Rivinus. The long and long 

 process (processus gracilis ; d) (commonly broken off in removal) is pr 

 during infancy a slender flattened 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 most frequently 

 converted into a fibrous band ; and in cases where the osseous pro- 

 cess persists, it is joined with the surrounding bone, and cannot be 

 separated. 



The INCCS is a flattened bone (fig. 298), and consists of a body incus: 

 and two processes. The body (b} is hollowed at the fore part (a) to body; 



