CHAPTEE VI. 



Vessels. Arteries. Veins. Capillaries, 

 and Lymphatics. 



VESSELS are of two species : blood-vessels and lyni- classification 

 phatics. Tlie former are sub-divided into arteries, 

 capillaries, and veins ; the latter into lymphatics, pro- 

 perly so called, and lacteals. The structure of arte- 

 ries, veins, the larger lymphatics, and lacteals, is 

 almost identical ; the same is true of the capillaries 

 and smaller lymphatic vessels, 



Each one of the tissues which we have studied thus 

 far has some special or characteristic element; but 

 this is not the case with the organs now under exa- 

 mination. No anatomical element of determinate 

 form belongs exclusively to them ; but that which 

 serves to distinguish them from other tissues, is the 

 peculiar arrangement of the several parts of which 

 they are- composed. 



Both recent and dried specimens are required for Preparations. 

 the examination of their structure. From portions 

 of dried vessels, very delicate and thin slices are cut 

 by a razor, and soaked in water before being placed 

 under the microscope. These sections answer for the 

 examination of the outer and middle coats, and for 

 the deeper portions of the internal coat of large ves- 

 sels ; but when we wish to study the epithelial layer, 



