AND PHYSIOLOGY. 



391 



Fig. 360. Fig. 361. 



a J> 



A B 



Membrana Tympani from the Outer (A), and from Small Bones of the Ear. a 9 The 

 the Inner (B) Sides. 1, Membrana Tympani. 2, Mai- Malleus, b, The Incus, c, The 

 leus. 3, Stapes. 4, Incus. Lenticular Bone, d, The Stapes. 



required. This cavity contains the " little bones of hearing/ 7 

 as they are sometimes called. These are the Malleus, a ham- 

 mer, — the Incus, an anvil, — and the Stapes, a stirrup, be- 

 cause they somewhat resemble these instruments. The Mal- 

 ♦leus lies directly against the drum of the ear (Membrana 

 Tympani), its opposite side connecting with the Incus, which 

 is in connection with the end of the Stapes, thus forming a 

 continuous chain of bones through the Tympanic Cavity. In 

 the walls of the Tympanum are no less than ten openings, 

 the most important of which are, one downwards into the 

 Pharynx known as the Eustachian Tube, another into the 

 Labyrinth, which is closed by the foot of the Stapes, and an- 

 other outwards to the External Ear. 



717. Labyrinth.— Cochlea.— Semicircular Canals — 

 Perilymph . — V estibu I c , — The Internal Ear is called a Laby- 

 rinth because of its very complicated structure and func- 

 tions. (Fig. 362, p. 392.) It mainly consists of a series of 

 semicircular canals and cavities, of which some are made up 

 of cartilage, and others of bone. The canals are composed of 

 bone, three in number, and their respective planes arranged at 

 right angles to each other. They contain the nerves of hear- 

 ing and other substances, which facilitate the transmission of 

 sound. One of these portions is named the Cochlea, because 



What are the names of the bones of the ear ? How many openings are there in the 

 tympanum ? T17. What is the labyrinth? Of what is it mainly made up ? 



