DISTRIBUTION OF BLOOD VESSELS. 201 



is conducive to their mutual strength: for the fibres of each 

 intermix and even co-operate in their actions, and both cir- 

 culations are carried on at the same time; that is, both ven- 

 tricles contract or close at the same instant; and the same 

 applies to the auricles. The blood which has just returned 

 from the body, and that from the lungs, the former by the 

 venae cavic, the latter by the pulmonary veins, fdl their re- 

 spective auricles at the same instant; and both auricles, con- 

 tracting at the same moment, discharge their contents simul- 

 taneously into their respective ventricles. In the like 

 manner, at the moment when the left ventricle is propelling 

 its aerated blood into the aorta, for the purposes of general 

 nutrition, the right ventricle is likewise driving the vitiated 

 blood into the pulmonary artery, in order that it may be pu- 

 rified by the influence of the air. Thus, the same blood 

 which, during the interval of one pulsation, was circulating 

 through the lungs, is, in the next, circulating through tiie 

 body; and thus do the contractions of the veins, auricles, 

 ventricles, and arteries, all concur in the same general end, 

 and establish the most beautiful and perfect harmony of ac- 

 tion.* 



§ 4. Distribution of Blood Vessels, 



In the distribution of the arteries in the animal system, 

 we meet with numberless proofs of wise and j)rovident ar- 

 rangement. The great trunks of both arteries and veins, 

 which carry on the circulation in the limbs, are conducted 

 always on the interior sides, and along the interior angles 

 of the joints, and generally seek the protection of the adja- 



* Evidence is afforded of the human conformation being expressly adapted 

 to tlie erect position of the bod}' by the position of the heart, as compared 

 with quadrupeds; for, in the latter, the heart is placed directly in the middle 

 of the chest, with the point towards the abdomen, and not occupying- any 

 portion of the diaphragm; but, in man, the heart lies obliquely on the dia- 

 phragm, with the apex turned towards the left side. 



Vol. II. 2r> 



