384 VETERiNARY LECTURES 



THE EAR. 



646. In the horse, the ears should be fine, and well pointed 

 forward, and when at work, should always be on the move, first 

 backward, and then forward, so as to catch sounds. Each ear is 

 made up of three distinct portions — i.e., the external ear, the middle 

 ear, and the internal ear. 



647. The External Ear is made up of three pieces of cartilage : 



1. Conchal, which forms the point. 



2. Annular, ring-shaped at the bottom. 



3. Scutiform, triangular in form, and which acts as a lever to 



move the conchal. 



These are all covered internally by a fine skin, containing minute 

 glands, which secrete wax, so as to prevent insects and other foreign 

 bodies entering the ear. 



648. The Middle Ear, or tympanum, contains four small bones, 

 named: (1) Malleus, or hammer; (2) incus, or anvil; (3) stapes, or 

 stirrup ; (4) os orbicular e (the smallest bone in the body). 



649. The Tympanum cavity is separated from that of the 

 external ear by a thin membrane known as the membrana tympani, 

 or drum of the ear. Sound waves produce vibration of this mem- 

 brane. These vibrations are communicated to the chain of small 

 bones above mentioned, and, by them, to the internal ear. In order 

 that the pressure on the two sides of the membrana tympani may be 

 maintained in a uniform condition, the cavity of the tympanum is 

 placed in communication with the pharynx by means of a tube, 

 known as the Eustachian tube. 



650. The Internal Ear is very complex. It is called the 

 labyrinth, and is made up of bony and membranous parts. The bony 

 part contains: (1) The vestibule; (2) semicircular canals; (3) cochlea, 

 or shell. The membranous part is contained within the bony portion, 

 and is specially adapted for hearing. 



