304 GENERAL ANATOMY. 



through branches and anastomoses, and a collateral circulation 

 is established. 



The inferior vena cava has been found obliterated, either 

 under, or even on a level with the subhepatic veins, and the 

 blood passing through the vena azygos; one of the primitive 

 iliac veins, one of the jugular veins, &c. have been several 

 times found obliterated. Four times I have seen the trunk of 

 the crural vein obliterated in the groin, and in every instance 

 the circulation was easily carried on by collateral passages. 

 Hunter once observed the superior vena cava and the left 

 bracio-cephalic vein almost entirely destroyed by the pressure 

 caused by an aneurism. I have seen a case, however, in which 

 the superior vena cava and its branches were filled with 

 plastic matter, and impermeable to blood, and in which death 

 appeared to have been the result of this alteration. I have 

 remarked several times, but not always, great serous infiltra- 

 tions coinciding with the obliteration of the veins. 



457. Small, hard and round bodies are sometimes found 

 in the veins, which on a superficial observation might be taken 

 for accidental osseous productions. Some writers have even 

 supposed that they were at first formed in the parietes of the 

 veins, in the edge of their valves, or even on the exterior of 

 these vessels; but this is not true. They are concretions, phle- 

 bolites, from the size of a grain of millet to that of a pea, of 

 various consistence, formed of superincumbent layers, inclosed 

 in the coagulated fibrinous blood, and often lodged in the lateral 

 dilatations of the veins where the blood stagnates, or in the 

 varicose veins, and always in the depending veins. The veins 

 in which they are, in fact, most commonly met with, are those 

 of the anus, the neck of the bladder, the uterus, the ovaries, 

 the testicles, and sometimes even the subcutaneous veins of 

 the leg. 



The hexathyridium or polystoma venarum of which 

 Treutler found two in the ruptured tibial vein of a man, who 

 had been washing in a river, seems to be an aquatic worm, a 

 planaria, which had found its way in it, and not an (ento- 

 zoaire) cntozoary. 



