242 GENERAL ANATOMY. 



in the divisions of which we, in like manner, generally find 

 acute angles, some right angles, and even some obtuse ones. 



356. The branches of the different parts of the vascular 

 system, at the same times that they divide or ramify, in pro- 

 portion as they are removed from the centre of the system, 

 nevertheless conimunicate or anastomose with each other. The 

 lymphatic vessels are those which have the greatest number of 

 these communications; in the veins there are a great many, in 

 the arteries there are fewer, and nevertheless they possess a 

 considerable number. These anastomoses occur by the union 

 of two vessels of the same kind, and of an equal volume or 

 calibre. 



In some parts, two vessels approach each other obliquely, 

 unite in a single trunk, which follows the mean direction of 

 the two vessels; such is the union of the two vertebral arteries, 

 in order to form the basilar artery, that of the anterior spinal 

 arteries, that of the aorta, and of the pulmonary artery in the 

 foetus, that of a great many veins, &c. 



Generally, vessels anastomose in such a manner as to form 



by their union an arch, from the convexity of which arise 



many branches; this arrangement is observed in the rnesente- 



ric or intestinal vessels, about the articulations, in the hand, 



* in the foot, &c. 



In other places two vessels, each following its direction, 

 communicate by a transverse branch; such is, for instance, the 

 communication between the umbilical arteries in the placenta; 

 such are those of the brain, of the right with the left side, and 

 of the anterior with the posterior part; such are also those of a 

 great many veins and arteries of the limbs. 



In several places, these various and more or less numerous 

 communications form circles or polygons, like the circle of 

 Willis, at. the base of the brain; those of the iris and mouth, 

 that which encircles the stomach, &c. 



In a great number of parts, or almost every way, the vessels 

 which anastomose in an arch, uniting likewise with others 

 proceeding from branches, some being near, and others far- 

 ther removed from the centre of the vascular system, establish 

 collateral ways of circulation: thus, for instance, the circum- 



