46 SCIENTIFIC HORSESHOEING. 



pending upon the function which the tissue has to perform. 

 If this is great, as in the more sensitive parts of the foot, a large 

 amount of blood is required, if the labor is a less exciting one, 

 as in the cartilages, and ligaments or membranes, the nutrition 

 is furnished by imbibing the fluids brought to the surface by 

 blood-vessels. The blood is carried from the heart to the vari- 

 ous organs by the arteries or their small terminations, and is 

 named red or arterial blood. The veins of sfeneral circulation 

 bring the nutritive fluid back to the heart, and, according 

 to its tint, it is named dark colored or venous blood. Both 

 systems present at their extremities innumerable branches, 

 which finally join each other, so that the fluid they carry 

 passes from one to the other in a constant or circular di- 

 rection. Between the two are small delicate networks of ves- 

 sels called capillaries, which subdivide into a regular lacework 

 so as to reach the neighborhood of every element. 



Nerve Supply. — The amount of blood, under normal con- 

 ditions is governed by nerves of the sympathetic system 

 which regulate the conditions of repose and activity. The 

 nerves issue from the cranium and branch into all the organs 

 like the arteries which they generally accompany. They fur- 

 nish the stimulus to animal life, and in the digits are the 

 essential instruments of touch or sensation. Three branches 

 of the internal and external plantar nerves furnish the foot on 

 each side, and accompany the digital artery and vein, which at 

 some points they cover with their divisions. The order of their 

 distribution and termination, together with that relating to 

 the circulatory system of the foot generally, will be clearly 

 comprehended by a glance at the several colored plates illus- 

 trating this section. 



Horny Tissues. — The hoof of the horse — considered as a 

 whole — represents the horny outer covering, completing the ex- 



