CIRCULATORY SYSTEM. 207 



OF THE VEINS. 



There are ten radical veins, though no more than two of 

 them possess a volume correspondent with the main arterial 

 trunk : these two, denominated the vena cava, may be looked 

 upon as the fellow-vessels of the anterior and posterior aortae : the 

 other eight are the 



PULMONARY VEINS ; 



Which vessels originate within the air-cells of the lungs, from the 

 extreme ramifications of the pulmonary artery, and, by repeated 

 and reiterated union and coalescence, at length form themselves 

 into eight venous trunks, which proceed directly from the roots of 

 the lungs to the left auricle of the heart, and into that cavity 

 empty themselves by four openings*. 



VENiE CAVJE, 



Anterior and Posterior, form the two main or general trunks 

 of the venous system ; the former receiving the blood returned 

 from the fore parts of the body ; the other, that flowing from the 

 hinder parts. Their ramifications in most parts exceed, in num- 

 ber and size, those of the correspondent arteries ; in addition to 

 which, veins are found in many parts (and those mostly super- 

 ficial) where arterial trunks do not exist ; which excess of number 

 and duplicity of course has caused a division of the veins into 

 those that are superficial, and those that are deep-seated. 



* The English veterinary professors reckon eight pulmonary veins ; the 

 French, but four. The disas^reement arises from the former reckoning 

 being made at the issue of the veins out of the substance of the lungs, 

 and the latter being taken from their termination in the cavity of the left 

 auricle. 



