118 



ANATOMY FOE NUESES. 



[CHAP. X. 



into the flattened cells which compose the wall of the capillaries, and which 

 form the lining membrane of the arteries and veins. The remaining coats 



P 



FIG. 83. ISOLATED CAPILLARY NETWORK FORMED BY THE JUNCTION OP 

 SEVERAL HOLLOWED-OUT CELLS, AND CONTAINING COLOURED BLOOD-CORPUSCLES 

 IN A CLEAR FLUID, p, p, pointed cell-processes extending in different directions 

 for union with neighbouring capillaries. 



of the larger vessels are developed later from other cells which apply them- 

 selves to the exterior of these tubes. 



The first white corpuscles do not appear in the vessels so early as the 

 coloured ones. They probably occur in the beginning as free cells and 

 wander in from the outside. 



The new vessels which form in the healing of wounds and in the restora- 

 tion of lost parts are produced by a process which is essentially the same as 

 above described. Blood-corpuscles, however, are not produced within them, 

 and it is still a matter of doubt as to where and how the red corpuscles 

 originate after birth. The white corpuscles are undoubtedly produced to a 

 large extent in the lymphatic glands and other lyrnphoid structures. 



