THE VASCULAR SYSTEM 



The capillaries branch and anastomose with one another to 

 form networks, the outlines of whose meshes vary according to 

 the tissue in which they occur. In such fibrous tissues as muscle 



and nerve they form elon- 

 gated meshes whose long 

 axes are parallel to those 

 of the muscle or nerve 

 fibres ; in the looser, more 

 areolar tissues they form 

 large meshes of irregular 

 form; while in the capil- 

 lary membranes, as in the 

 walls of the pulmonary 

 alveoli, they are disposed 

 in a close net the diameter 

 of whose meshes scarcely 

 exceeds that of the capil- 

 laries. 



With but few excep- 

 tions capillaries occur in 

 all the tissues of the body. 

 In epithelium and in carti- 

 lage there are no blood 

 vessels of any kind, and 

 in the splenic pulp it is 

 doubtful if true capillaries 

 occur. In certain tissues 

 large vascular spaces occur, 

 which are comparable to 

 the capillaries in that their 

 wall consists of scarcely 



FIG. 93. Two SINUSOIDAL VESSELS FROM THE . , -1,11-1 



MEDULLA OF THE HUMAN ADRENAL. ^10 ^0,11 the Cndothelial 



Each contains the outline of a single red blood tube > but which differ from 

 cell for comparison of size. At a, a small vein is the true Capillaries in the 



8h T;JV S fil1 ^ f f th f ^ d /f P ssesse8 / extreme size of their lu- 



much thicker wall than that of the sinusoids. 



Hemateiu and eosin. x 410. men. These vessels have 



been described by Minot * 



as sinusoids. They are found in the erectile tissues, adrenals, 

 coccygeal gland, parathyroids, and heart, in the maternal placenta, 

 and in the fetal liver, pronephros, and Wolffian body. 



* J. Bost. Soc. of Med. So., 1900. 



