•The Vascular System. 



87 



head, ant.Hnibs 



THE VASCULAR SYSTEM. 



In the rabbit, as in all vertebrates, the vascular system 

 (Fig. 46) embraces a central, muscular organ of propulsion, the 

 PLAN OF THE ^^^^> '^"^ a series of branched tubes, the blood- 

 CIRCULATION. vessels, the latter being of three different kinds: 

 (a) thick-walled, elastic, distributing vessels — 

 arteries ; (b) microscopic terminal canals in the peripheral' organs — 

 capillaries ; and (c) thin-walled collecting vessels — veins. 



The chief mammalian feature in this system consists in the 

 division of the heart into two portions, 

 each cOTsisting" of a receiving chamber, or 

 atrium, and a driving chamber, or 

 ventricle, and the arrangement of their 

 vascular connections in such a way that 

 two complete circulations are establislied. 

 One of these is the long, or systemic 

 circulation. It is concerned witli the 

 distribution of blood to the various parts 

 of the body, with the exception of the lungs. 

 It is establislied by the left ventricle, the 

 aorta, the carotid and subclavian branches 

 of its arch, and the parietal and visceral 

 branches of its thoracic and abdominal 

 portions. The blood is collected from the 

 anterior portions of the body through 

 paired internal and external jugular and 

 subclavian veins, communicating with the 

 right atrium of the heart through paired 

 ' superior cavals ; from the posterior portions 



of the body through the unpaired and also asymmetrical inferior 

 caval vein, the latter passing forward on the right of the median 

 plane and entering the posterior end of the right atrium. 'The 

 Second, short, or pulmonary circulation, is concerned with 

 the distribution of the blood to the lungs for purposes of aeration. 

 It is established by the right ventricle, the pulmonary artery and 

 •its paired branches, and by the capillaries of the lungs. The blood 

 is delivered to the left atrium through several pulmonary veins. 



portal, 



Body atnU, post limha 



Fig. 46. The mammalian 

 circulation, rv, Iv, right and 

 left ventricles; ra, la, right and 

 left atria; sc, sp, semilunar 

 valves of aorta and pulmonary 

 artery; vt. vm, right and left 

 atrioventricular valves. 



