18 STRUCTURE AND ECONOMY OF THE HORSE. 



Avays, SO as to admit of motion : in many we have the form of a 

 hin2;e ; in others that of a ball and socket. 



The motion of the limbs is effected by means of the mnscles 

 or flesh, which, although to a casual observer appearing as a 

 homogeneous mass, is readily separable into a greater number of 

 distinct bodies of various forms and sizes. These muscles have 

 commonly two separate attachments, which are usually bones, 

 and, by contracting in length, they bring these points of attach- 

 ment nearer to each other. Muscles arc composed of a vast 

 number of fibres, which, on being acted on by nervous influence, 

 diminish in length and increase in bulk, and thereby approxi- 

 mate the different objects to which they are attached. They are 

 usually fastened to bones by means of a strong white substance 

 called tendon, which, however, possesses in itself no power of 

 contraction, but merely communicates the contractile force to 

 the object to be acted on. Where the two objects of attachment 

 are distant from each other, the greater portion of the distance 

 is occupied by the tendons, the advantage of which is obtained 

 from their diminished size in proportion to their strength : thus 

 Ave find the leofs of horses below the knee are li^ht and slender, 

 from the absence of muscular and the substitution of tendinous 

 substance. The greater part of the muscles are voluntary, being 

 under the control of the mind ; but some are involuntary, such 

 as the heart and the diaphragm. 



Muscles are extensively supplied with vessels of various kinds, 

 such as arteries for their nourishment, and veins for the return 

 of the blood after this purpose is effected. There are likewise 

 nerves, which not only furnish sensation, but also communicate 

 to the muscles the mandates of the will. 



These nerves proceed either from the brain or its continuation, 

 the spinal cord, which may be considered as the fountain of sen- 

 sation, and the residence of the mind ; and thus sensation is first 

 sent from the extremities to the brain by the nerves, and then 

 by another set of nerves the will is conveyed to the muscles. 



The brain is a soft pulpy substance contained within the head, 

 and the spinal cord is somewhat similar in appearance, and 

 extends from the brain to the tail, through a hole in the bones 

 Avhich form the spinal column. 



The body is divided into two principal cavities, the chest and 

 the abdomen ; and separated by a muscular partition called the 

 diaphragm. The former contains the lungs and heart, Avhose 

 uses are to purify and distribute the blood by means of the func- 

 tions of respiration and the circulation ; and the latter caA^ity 

 contains the stomach and boAvels, in Avhich the functions of di- 

 gestion are carried on, besides several important glands, such as 

 the liver, kidney, and pancreas, and other supplementary parts. 



The food having been Avell triturated by the teeth, and mixed 



