THE BLOODVESSELS. 



57 



vary in size in the different vascular tissues : they are very large in 

 bones, and smallest in the lungs and in the brain. The smallest capil- 

 laries, however, admit the little bodies which are found in the blood, 

 called the red blood-corpuscles. Tissues which are destitute of capil- 



Fig. 35. 



Fig. 35. a (Kolliker), capillaries of muscle, forming long meshes, b (The Author), capillaries of a smooth 

 mucous membrane, forming large polygonal meshes. Moderately magnified. 



Fig. 36. 



Fig. 37. 



Fig. 36. a (Berres), capillaries of the papillae of the skin of the tip of the finger, forming single loops. & 

 (Berres), capillaries of the villi or little projections of the mucous membrane of the small intestine, form- 

 ing small meshes. Moderately magnified. 



Fig. 37. (Quekett.) Capillaries of the terminal extremity of a duct of the parotid gland, forming very 

 close meshes. Moderately magnified. 



lary vessels, such as the cartilages of the joints, certain transparent 

 parts of the eyeball, including the clear coat or cornea, the substance 

 of the teeth, the epithelial tissues, and the cuticle or outer skin and 

 its appendages, the nails and hairs, are called non-vascular. 



When a capillary vessel is very highly magnified, as in Fig. 38, its 

 walls are seen to be exceedingly thin and delicate, and to be composed 

 of homogeneous membrane in which many nuclei are set: on approach- 

 ing the smallest arteries and veins, the capillaries gradually acquire 

 extra coats and so pass into those vessels. The walls of all these 

 small vessels are of course without vasa vasorum. 



The blood. The blood, the fluid contents of the bloodvessels, is of 

 a bright florid color in the arteries, and of a dark purple tint in the 

 veins. It is, apparently, a red homogeneous solution, but it really 

 consists of a clear, limpid, almost colorless liquid, named the liquor 

 sanguinis, the liquor or plasma of the blood, and of certain floating 

 particles called blood-corpuscles. These latter are of two kinds, the 

 red or colored corpuscles, and the white corpuscles. Blood also con- 

 tains albuminous granules and fat particles, besides other occasional 



