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CHAPTER IV. 



SKETCH OF THE ANATOMY OF THE HORSE. 



Definitions — Bones — Joints and Ligaments — Muscles — Heart and Lungs — 

 Nervous System of the Horse. 



Definitions. — ^^'hen one bone unites with another bone, or with a 

 piece of cartilage, to form a joint, it is said to articulate with it. The 

 term articulation is used as a synonym for Joint. 



A ball and socket joint is formed by the head of one bone resting in 

 a cavity of another bone. The more shallow the cavity, the more ex- 

 tensive will be the power of movement. The horse's shoulder joint and hip 

 joint are good examples of this kind of articulation. A hinge joint is one 

 which w^orks only by extension and flexion, like the horse's knee. 



" A limb," as Professor Huxley states, " is, flexed when it is bent; extended, 

 when it is straightened out." We may adopt this definition, with the ex- 

 ception that the fetlock joint becomes bent when it is extended, and 

 straightened out when it is partly flexed. 



The word dorsal is used with reference to things of, or belonging to, the 

 back, which, anatomically, is limited to that portion of the spine which is 

 connected with the ribs. 



If a muscle is attached, by one end, to a bone which it can move, and, 

 by the other end, to one which is fixed, the former is called the insertio?i of 

 the muscle ; the latter, the origin. Thus, the origin of the biceps in man [see 

 p. 12) is near the shoulder joint; and its insertion is on the bone of the 

 forearm. When a muscle, on contracting, can move the bones at both its 

 ends, the points of connection are called attachments ; an expression which is 

 also applied collectively to the origin and insertion. I may mention that 

 muscles are not invariably attached to bones, but may, on the contrary, be 



