CAPILLARY BLOOD-VESSELS AND LYMPHATICS. 



115 



current is very rapid in the small arteries, somewhat less so in the 

 veins, and comparatively slow in the capillaries. The current is fastest 

 in the centre of the vessel, slowest near the wall (inert layer), and 

 with care it may be observed especially where there is any commen- 

 cing inflammation of the part, as in the mesentery in consequence of 

 exposure that the white blood-corpuscles, which always tend to 



FIG. 139. CAPILLARY VKSSKLS FROM 

 THE BLADDER OF THE CAT, MAGNI- 

 FIED. 



The outlines of the cells are stained by 

 nitrate of silver. 



FIG. 140. CAPILLARY BLOOD- 

 VESSELS IN THE WEB OF A 

 FROG'S FOOT, AS SEEN WITH 

 THE MICROSCOPE. (A. Thom- 

 son.) 



The arrows indicate the course of the 

 blood. 



pass into the inert layer, and to adhere occasionally to the inner surface 

 of the blood-vessels, here and there pass through the coats of the small 

 vessels, and appear as migratory cells in the surrounding connective tissue. 



LYMPHATIC SYSTEM. 



To the lymphatic system belong not only the lymphatic vessels and 

 lymphatic glands, but also the cavities of the serous membranes, which are 

 moistened with lymph and are in open communication with the 

 lymphatic vessels in their parietes. 



The larger lymphatic vessels somewhat resemble the veins in struc- 

 ture, except that their coats are much thinner and their valves much 

 more numerous. In lymphatics of somewhat smaller size, the wall of 

 the vessel is formed, first, by a lining of pavement-epithelium cells 

 (lymphatic endothelium), which are elongated in the direction of the 

 axis of the vessel ; and, secondly, by a layer of circularly and obliquely 

 disposed muscular fibres. In the smallest vessels (lymphatic capillaries, 

 which, however, are generally considerably larger than the blood-capil- 



