LESSON n 



THE ORGANS OF CIRCULATION 



Part I.- 



-The Blood Vascular System and the 

 Circulation 



1. The Capillaries. —Almost all parts of the body are 



vuscvlar ; that is to say, they are traversed by minute and 

 very close-set canals, which open into one another so as to 

 constitute a small-meshed network, and confer upon these 

 parts a spongy texture. The canals, or rather tubes, are 

 provided with distinct but very delicate walls, composed of 

 what at first sight appears to be a structureless membrane, 



d— 



Fio. 7. — Capillaries. 



A, surface view ; B, cut lengthwise ; C, cut across ; e c, enduthelial cells ; 

 n, nuclei ; d, the lumen or bore. 



