22O 



THE CIRCULATORY SYSTEM. 



[CH. xvin. 



of the intestines; among the largest, those of the skin, lungs, and 

 especially those of the medulla of bones. 



The size of capillaries varies necessarily in different animals in 



Fig. 223. Capillary blood-vessels from the omentum of rabbit, showing the nucleated 

 endothelial membrane of which they are composed. (Klein and Noble Smith.) 



relation to the size of their blood-corpuscles : thus, in the Proteus, 

 the capillary circulation can just be discerned with the naked eye. 



Fig. 224. Network of capillary ves- 

 sels of the air-cells of the horse's 

 lung magnified, a, a, capillaries 

 proceeding from b, l>, terminal 

 branches of the pulmonary ar- 

 tery. (Frey.) 



Fig 1 . 225. Injected capil- 

 lary vessels of muscle 

 seen with a low mag- 

 nifying power. 



(Sharpey.) 



The form of the capillary network presents considerable variety 

 in the different tissues of the body : the varieties consist 

 principally of modifications of two chief kinds of mesh, the 

 rounded and the elongated. That kind in which the meshes or 



