268 

 THE EAR. 



641. 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 Eav, the Middle Ear, and the Internal 

 Ear. 



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



ist.~Conchal, which forms the point. 



2nd. — Annular, ring-shaped at the bottom. 



3rd. — 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. 



643. The Middle Ear, or Tynipanuni, contains four small bones, 

 named: i. — Malleus or Hammer; 2. — Incus or Anvil; 3. — -Stapes or 

 Stirrup ; 4. — Os-orhiculare (the smallest bone in the body). 



644. The Tympanum cavity is separated from that of the external 

 ear by a thin membrane known as the Membrane Tympania, or drum 

 of the ear. Sound waves produce vibration of this membrane. 

 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 membrane tympani may be maintained 

 in an uniform condition, the cavity of the tympanum is placed in 

 communication with the pharynx by means of a tube, known as the 

 Eustachian Tube. 



645. The Internal Ear is very complex. It is called the labyrinth, 

 and is made up of bony and membranous parts. The bony part 

 contains: T. — The Vestibule; 2. — Semi-circular Canals; 3. — Cochlea, ov 

 shell. The membranous part is contained within the bony portion and 

 is specially adapted for hearing. 



