BLOOD-VESSELS. 53 



In addition to the blood-vessels care other tubes, which con- 

 tain a yellow or yellowish-red fiiiid. These have very thin 

 walls, are small, and usually accompany veins, into which they 

 finally pour their contents. The fluid is termed lymph, and 

 the vessels themselves lymph-vessels. Such vessels can be 

 found in the foot, but are so attenuated as scarcely to be 

 visible. A lengthened description would be inappropriate here. 

 A few remarks on the blood-vessels must suffice. 



At their origin from the heart the arteries are large and 

 thick-walled, but, as they recede from this point, they continu- 

 ously divide, and their walls become thinner. Large stems 

 branch off into smaller ; from these twigs originate in all direc- 

 tions until, finally, all trace of them appears to be lost in the 

 surrounding tissues. The arrangement can best be compared 

 to a tree, the trunk of which divides into main stems, the stems 

 into branches, and the branches into innumerable twigs. The 

 splitting up of the vessels which provide blood for the organs 

 of the body ultimately produces a net-work, which can no longer 

 be distinguished wdth the naked eye. The minute vessels of 

 this net-work are termed capillaries. The capillaries, after a 

 short course, re-unite in the same fashion as they had arisen 

 from the arteries, — that is, by their union they gradually form 

 larger and larger vessels, termed veins, which at last empty into 

 the heart. The veins, more especially those of the limbs, have 

 valves which support the column of blood ascending against the 

 action of gravity. The course of the veins is precisely com- 

 parable to that of tfegi arteries, though in them the blood flows 

 in an opposite direction. 



The arteries and veins being the conductors of blood to 

 and from the various organs are of great importance, but the 

 capillaries are equally indispensable to nutrition and secretion. 

 Passing through their thin walls the fluid portions of the bright 

 red arterial blood bathe the tissues of the different organs, bring- 

 ing to each the material necessary for its existence and function. 



All parts of the foot are provided with blood-vessels and 

 contain more or less blood, with the single exception of the 

 horny tissues. The parts, however, concerned in producing 

 horn, receive a large supply, and are the most vascular parts 

 of the entire foot. 



