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CHAPTER VI. 

 OF THE VEINS. 



THE veins are the vessels which return the blood to the auricles of 

 the heart, after it has been circulated by the arteries through the va- 

 rious tissues of the body. They are much thinner in structure than 

 the arteries, so that when emptied of their blood they become flat- 

 tened and collapsed. The veins of the systemic circulation convey 

 the dark-coloured and impure or venous blood from the capillary system 

 to the right auricle of the heart, and they are found after death to be 

 more or less distended with that fluid. The veins of the pulmonary 

 circulation resemble the arteries of the systemic circulation in contain- 

 ing during life the pure or arterial blood, which they transmit from 

 the capillaries of the lungs to the left auricle. 



The veins commence by minute radicles in the capillaries which are 

 everywhere distributed through the textures of the body, and con- 

 verge to constitute larger and larger branches, till they terminate in 

 the large trunks which convey the venous blood directly to the heart. 

 In diameter they are larger than the arteries, and like those vessels 

 their combined areae would constitute an imaginary cone, whereof the 

 apex is placed at the heart, and the base at the surface of the body. 

 It follows from this arrangement, that the blood in returning to the 

 heart is passing from a larger into a smaller channel, and therefore 

 that it increases in rapidity during its course. 



Veins admit of a threefold division, into superficial, deep, and 

 sinuses. 



The Superficial veins return the blood from the integument and su- 

 perficial structures, and take their course between the layers of the 

 superficial fascia ; they then pierce the deep fascia in the most con- 

 venient and protected situations, and terminate in the deep veins. 

 They are unaccompanied by arteries, and are the vessels usually se- 

 lected for venesection. 



The Deep veins are situated among the deeper structures of the body 

 and generally in relation with the arteries ; in the limbs they are en- 

 closed in the same sheath with those vessels, and they return the 

 venous blood from the capillaries of the deep tissues. In company 

 with all the smaller, and also with the secondary arteries, as the 

 brachial, radial, and ulnar in the upper, and the tibial and peroneal in 

 the lower extremity, there are two veins, placed one on each side of 



