GENERAL CONSIDERATIONS. 



603 



are submitted. But these anastomoses, if they offer this immense advantage^ 

 have also their inconveniences : we refer to the difficulties experienced in arresting- 

 hfemorrhage in wounds of certain organs, owing to the relations of the principal 

 vessel with its communicating collaterals. 



Mode of Distribution. — The branches an artery distributes in the neigh- 

 bouring organs are distinguished as terminal and colluteruJ. The arteries, after 

 pursuing a certain course, divide into several branches — nearly always two, which, 

 as new arteries, continue the original vessel and take the name of terminal 

 branches, because they really begin at the terminal extremity of that vessel. 



The collateral vessels arise at various distances along the course of the arteries, 



Fig. 360. 



WEB OF frog's foot STRETCHING BETWEEN TWO TOES, SHOWING THE BLOOD-VESSELS 

 AND THEIR ANASTOMOSES. 



a, a, Veins ; b, b, b, arteries, the capillaries being between. 



and proceed in a lateral direction ; they increase in number as the arteries become 

 more supei-ficial. 



The distinction between the terminal and collateral branches of arteries is not 

 always easy to establish, and is far from having an absolute value ; it possesses, 

 nevertheless, some importance, as it greatly facilitates description. 



Termination. — Arteries terminate in the substance of the tissues by ex- 

 tremely line and numerous ramuscules, which so frequently anastomose with each 

 other as to form a plexus or microscopical network, the meshes of which are very 

 close. These constitute the capillary system, which again gives rise to ramifica- 

 tions of gradually increasing size — the veins. The capillary system is, therefore, 

 nothing more than a network of microscopical canals intermediate to the arteries 

 and veins. 



In the erectile tissues, the mode of termination is different ; the small arteries 

 sometimes opening directly into the cells placed at the origin of the veins, without 

 passing through a capillary plexus. In describing the genital organs, we shall 

 notice, in detail, the termination of the arteries in the cavernous tissues. 



Structure. — The walls of arteries offer a certain rigidity, which permits 



