THE VENOUS SYSTEM. 359 



single large artery in man, to which a corresponding 

 branch might not be found in birds ; and on the other 

 hand, that there is perhaps no artery in the bird, to 

 which there is not an analogous branch in man. The 

 chief difference consists in the relative sizes of the sev- 

 eral trunks ; but these correspond closely with the 

 amount of tissue they have respectively to supply. 

 Here, then, we have an example of the Unity of De- 

 sign, which we see every where prevalent throughout 

 Nature, manifesting itself in the close conformity of a 

 great number of apparently different structures, to one 

 general plan, while there is, at the same time, an almost 

 infinite variety in the details." 



THE VENOUS SYSTEM. 



The arteries, as we have seen, transmit the blood to 

 every part of the system by the contractile force of the 

 heart. All the large arteries are deeply situated, that is, 

 none of them lie near the surface of the body. We 

 may observe here protective care and design, since a 

 wounded artery of any considerable size is always at- 

 tended with danger, in consequence of the force with 

 which the heart propels the blood through it ; but, being 

 deeply seated, accidents to them are of course much less 

 common than they would be were they situated, like the 

 veins, near the surface. When an artery is wounded, 

 the blood spouts out by jets, with great force, and is of a 

 light vermilion color. If a vein of the same size be 

 wounded, the blood merely flows out, unless the passage 

 towards the heart is interrupted by a ligature, as pre- 

 paratory to blood-letting, when it runs in a continued 

 stream, but not in interrupted jets, occasioned by the 

 motion of the heart, as in lesions of an artery. This 

 difference of the manner in which blood flows from arte- 

 ries and veins should be remembered, since life may 

 sometimes depend thereon. If the blood flows in jets, 

 and in considerable quantity, there is danger, and the 

 attendants ought to press upon the part, perhaps with the 

 thumb, until proper assistance can be obtained. The 

 wound of a vein is attended with much less danger, and 



