35 



CHAPTER IV. 



SKETCH OF THE ANATOMY OF THE HORSE. 



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

 System — Teeth. 



Definitions. — When 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 works 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 exception that the fetlock joint becomes bent when it is extended, 

 and straightened out when it is partly flexed. 



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 insertion 

 of the muscle ; the latter, the origin. Thus, the origin of the biceps in 

 man (p. 28) is near the shoulder joint ; and its insertion is on the bone 

 of the fore-arm. 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. 

 Muscles are not invariably attached to bones, but may, on the con- 

 trary, be connected to cartilages, ligaments, fibrous covering of muscles, 

 or even to the skin. 



Bones. — The skeleton is composed of the limbs, head, spinal 

 column, and its accessory bones (Fig. 18). A vertebra is one of the 

 short bones which form the spinal column that extends from the head 

 to the end of the tail. There are, as a rule, seven vertebrae of the neck, 

 eighteen of the back, six of the loins, five of the croup (sacrum), and 

 from thirteen to twenty of the tail. All the vertebrae, except those 



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