374 HISTOLOGY OF THE MORBID PROCESSES. 



any such demand, and continue without any such limitation. In 

 this way the vascular tumors, or angiomata, are produced. We 

 may regard them as springing, not from a single tissue or an adven- 

 titious combination of tissues, but from one of those anatomical 

 " systems " in which several tissues are normally associated in a 

 definite arrangement, and, under normal conditions, develop together 

 to form well-defined structures distributed throughout the body. 

 There are three such systems of associated tissues : the bloodvessels, 

 the lymphatic system, and the nervous system. Each of these may 

 enter into the formation of an apparently purposeless neoplasm, 

 forming the hsemangiomata, lymphangiomata, and neuromata. Of 

 these, the first two are of vascular character and mesodermic origin, 

 and their consideration naturally follows that of the other tumors 

 arising in tissues of similar embryonic origin. 



1. Hsemangioma. The bloodvessels entering into the formation 

 of hsemangiomata are usually relatively deficient in the develop- 

 ment of their muscular coats. They resemble large capillaries 

 which have been reinforced by a covering of fibrous tissue. The 

 vessels may lie with their walls almost in contact with each other, 

 or there may be a considerable amount of interstitial tissue between 

 them. It is not always possible to decide in a given case whether 

 the vessels are strictly of new formation or not. Masses consisting 

 essentially of bloodvessels may arise through dilatation of pre- 

 existent vessels, with atrophy of the tissues that normally lie be- 

 tween them. This is the origin of the angiomata of the liver, and 

 many of the angiomata of the skin (nsevi) are explicable in the 

 same manner. In the liver the capillaries of the lobules become 

 dilated and their walls thickened, the parenchymatous cells between 

 them disappearing by atrophy, and, as the capillary walls come in 

 contact and exert mutual pressure, they may undergo atrophy, per- 

 mitting a communication between their lumina, so that a spongy 

 mass of tissue results, with large cavities filled with blood (Fig. 

 339). Such "cavernous angiomata" hardly constitute tumors in the 

 restricted sense in which that term has been used hitherto. They 

 are rather ectatic states of the vessels normally present in the parts 

 where they are found. 



Somewhat more akin to the true tumors are the masses which 

 arise through elongation and widening of the vessels of a part 

 (aneurisma racemosa), for in this case there is a real reproduction 

 or growth of the vessels. 



