Elementary Anatomy of a Hound 43 



the middle coat is very thick, which is necessary to 

 withstand the blood-pressure. 



Some arteries and veins have nerves, others not. 



The veins are similar in structure to the arteries, 

 though with certain modifications. 



The hlood consists of two portions, viz., a solid 

 portion and a liquid one. 



The hlood globules or corpuscles represent the first 

 named, and the liquor sanguinis the latter. When 

 in the blood-vessels (during life) the blood never 

 coagulates unless a " clot " forms in a blood-vessel 

 as the result of disease, but such coagulation is con- 

 fined to one part of the blood-vessel and never 

 general. 



Outside the body the blood coagulates through 

 soUdification of the fibrin which is dissolved in the 

 plasma. This fibrin contracts subsequently, and 

 causes the blood to divide into two portions, viz., 

 the clot and the serum. The clot is red, but the 

 serum of a pale colour. 



The blood globules are of two kinds, viz., coloured 

 and colourless. It is the former that contain the 

 red-colouring matter of the blood and act as carriers 

 of oxygen. These corpuscles circulate towards the 

 centre of the blood-stream, whereas the colourless 

 ones occup3^ a position nearer to the wall of the 

 vessel, during circulation. 



The blood cells are very minute, consequently 



