FUNCTIONS OF TENDONS, BLOOD-VESSELS, AND NERVES. 91 



The bones and ligaments are set in movement by the 

 contraction of muscles ; and, though not with invariable 

 certainty, the result of such contraction may largely be deter- 

 mined by studying the position of the muscles themselves, and 

 the points at which their tendons are inserted. Owing to the 

 position of the muscles, much can be learnt of their functions 

 by studying living animals. We see, for instance, during 

 movement, a constant change of form in the more superficial 

 muscles. Sometimes the muscle becomes more, sometimes less 

 prominent. Each change is followed by movement of the 

 bones. As we see the bones of the foot move, though we are 

 aware this region possesses no muscles, it is easy to deduce 

 that such movement depends on muscular force developed in 

 other parts and transmitted by the tendons. The justness of 

 the conclusion is verified when muscles or tendons are injured. 

 Movement in the affected parts is then limited or altogether 

 inhibited, just as in ourselves the hand and fingers become 

 stiff after severe injuries of the muscles or tendons of the 

 fore-arm. 



The parts played by the blood-vessels and nerves are, at 

 first sight, obscure, and for many centuries remained unrecog- 

 nised. For our purpose it is quite sufficient to know that the 

 arteries carry bright red blood, the nutritive fiuid of the body, 

 to every part ; that this supplies nourishment to the tissues, 

 that from it are elaborated the secretions, and that the veins 

 again carry it off when exhausted. The return of blood from 

 the extensive venous net-works of the foot is greatly assisted 

 by the peculiar mechanical formation and the large amount of 

 elastic tissue within the hoof. 



Similarly, it is sufficient to know that the work of the 

 nerves is to control movement and secretion, to convey im- 

 pulses recognised by the brain as sensation, and to preside over 

 nutritive processes in particular organs. The nerves may be 

 likened to telegraph wires. Let us suppose that a certain 

 movement is contemplated ; at the right moment the muscles 

 involved are made aware, through the nerves, of the amount 

 of contraction required of them, information which is immedi- 

 ately followed by the execution of the movement. Wherever 

 a sensitive part, that is, one containing nerves, is touched or 

 injured, the brain or spinal cord receives an impression of 



