296 GENERAL ANATOMY. 



varies with age. This difference, moreover", is not the same 

 in all parts of the body. In the pulmonary system it does 

 not exist, for the veins are there apparently equal in capacity 

 to the arteries. This is also the case with the renal vessels. 

 In the testicles, on the contrary, the veins are greatly superior 

 to the arteries. 



444. The situation of the veins is generally the same as 

 that of the arteries, these two kinds of vessels accompanying 

 each other in their course, and uniting at their termination. 

 Almost every where, a trunk, a branch, or a twig of an artery, 

 is accompanied by one or two veins. There are, however, 

 exceptions: thus, in the cranium, the spine, the eye and liver, 

 the arteries and veins affect different situations and disposi- 

 tions; the vena azygos, the trunk of the intercostal veins in 

 the space between the pericardium and liver, is not accompa- 

 nied by an artery, and this is also the case with the subcutane- 

 ous veins. 



445. The veins commence by capillary or microscopic 

 radicles, forming a continuation of the ramuscules of the arte- 

 ries. These radicles are colourless or red, according as their 

 diameter admits a single series of globules, or several at once. 

 In some places, as in the intestine, the lungs, &c., the succes- 

 sive reunion of the radicles of the veins corresponding with, 

 and entirely similar to the divisions of the arterial ramuscules. 

 In other places the disposition is different. Without speaking 

 of the erectile or cavernous tissue, in which the swelling and 

 communication of the veins are extreme, in many other parts 

 they have different dispositions from those of the arteries: 

 they form plexuses at the neck of the bladder, in the spine, 

 and around the spermatic artery, wide canals in the spongy 

 bones, and under the skin, they form, by their numerous com- 

 munications, a great vascular net-work with angular, and most 

 ordinarily meshes. 



They are not so regularly cylindrical as the arteries, and so 

 far from following a regular order of increase in the volume 

 of the trunks and of decrease in their total capacity, very 

 large branches are sometimes seen connected with a trunk of 

 no great size, which depends especially on the softness of the 



