HEARING. 793 



which is the most important, is tense, strong, and fibrous, made up of cir- 

 cular and radiating fibres, with a small amount of elastic tissue intermixed. 

 698, In the internal wall of the tympanum are two small openings 

 the fenestra ovalis and fevestra rotunda which communicate with the laby- 

 rinth. The fenestra rotunda is closed by a membrane. Extending between 

 the tympanic membrane and the fenestra ovalis are the ossicles, consisting 

 of three small bones, which form a system of levers. These ossicles are 

 termed, from their resemblance to particular objects, the malleus, incus, and 

 stapes. (Fig. 185.) The malleus consists of a head, neck, long and short 

 process, and handle. The head articulates with the roof of the tympanum 

 and in a depression of the incus ; the handle is directed downward and 

 attached by its whole length to the tympanic membrane ; the long process 

 ( processus gracilts) is directed forward and has attached the insertion of the 

 laxator tympani muscle; the short process, which is at the base of the long 

 process, has attached the insertion of the tensor tympani muscle. The incus 

 consists of a body, a long and short process. The body of the incus has a 

 depression in which articulates the head of the malleus ; the short process 

 is attached to the posterior wall of the tympanum ; the long process (len- 

 ticular process) is placed almost vertically, and at its end is a rounded 



FIG. 188. 



Representation of the Semicircular Canals Enlarged. (From a model in University College 

 Museum.) a, superior vertical ; 6, posterior or inferior vertical ; and c, horizontal canal ; d, com- 

 mon opening of the two vertical canals ; e, part of the vestibular cavity ; /, opening of the aque- 

 duct of the vestibule. 



process (the os orbiculare}, which articulates with the head of the stapes. 

 The stapes consists of a head, neck, two crura, and a base. The head arti- 

 culates with the long process of the incus ; the neck serves as a point of in- 

 sertion of the stapedius muscle ; the crura diverge from the neck and unite 

 with the oval base at its greatest diameter. The base is fixed in the fe- 

 nestra ovalis by attachments formed by the lining membranes of both the 

 tympanum and internal ear. These ossicles are connected with each other 

 and to the walls of the tympanum by ligaments, and at their articulations 

 they are furnished with cartilages and synovial membranes. They are en- 

 veloped by prolongations of the mucous membrane lining the tympanum. 



699. The internal ear or labyrinth is the most essential portion of the 

 auditory apparatus. It consists of three portions the vestibule, semicircular 



