264 CIRCULATORY APPARATUS. 



said to exist. This at once does away with the complication 

 which played so weighty a part in the causation of aneurism. 

 The etiology of phlebectasy is obviously one and the same in all 

 cases, sc. mechanical dilatation in consequence of a local rise in 

 the blood-pressure ; and to this etiological monotony corresponds 

 an equal uniformity in the course of the anatomical alterations. 

 It is quite possible to find in dilatations of the veins the three 

 main forms which may result from the distension of a cylindrical 

 tube ; we may distinguish between cylindrical, fusiform and 

 saccular phlebectasy ; but such distinctions are here of trifling 

 value, simply because in most cases of phlebectasy all three 

 varieties coexist; indeed the disorder is never restricted to a 

 single and very marked dilatation of a vein, but always involves 

 the moderate dilatation of an entire plexus, or of all the branches 

 of a single trunk. 



Under normal conditions the pressure of the blood in the 

 venous system is so insignificant, that in the larger veins it 

 barely exceeds that of the atmosphere, and may even fall below 

 it in the immediate neighbourhood of the heart. Accordingly, 

 the walls of the veins are comparatively thin ; they are, so to 

 sa}^, only adapted to resist this moderate degree of pressure. 

 Should any circumstance raise the blood-pressure, the calibre 

 of the vein must necessarily increase, and its walls be put on the 

 stretch ; if the increased pressure continue, or even if it recur 

 periodically, the walls of the vein become permanently distended, 

 and phlebectasy is the result. 



§ 229. Phlebectasy, as might be supposed, begins in the im- 

 mediate neighbourhood of the valves. The sinuses just above 

 the valves are distended, and form small, nodular A^aricoslties 

 along the vein ; its superficial position enables them to be readily 

 distinguished through the skin. The valve-flaps tliemselves have 

 to support a greater weight than usual ; they finally become in- 

 competent, and the greater their incompetence, the farther does 

 the ectasy extend along the vein. At first, the vein is stretched 

 longitudinally ; inasmnch however as it is fixed at both ends and 

 cannot be sufficiently displaced, the elongated vessel must either 

 bend from side to side, forming zigzags, or become spirally 

 twisted. Both varieties occur, the zigzag in the larger, the spiral 

 in the smaller veins. The former serves as a transition to that 

 degree of phlebectasy whicli we call ^^ varicosity." The convexity 



