(•han(;es in fetal vessels of the liver 485 



instead of remaining straight or approximately so. The entire 

 absence of a fibrous substitute for the umbihcal vein in the sheep, 

 (log. etc., between the umbiUcus and the xiphoid process must, 

 it seems to me, })e due to the retraction of the vein and would 

 seem to suggest very strongly that Haberda is mistaken when 

 he says that the amount of retraction determines the length 

 of the fibrous filament. Moreover, it is not at all improbable 

 that the tension exerted by the retracting and degenerating 

 suspensory ligament is one of the factors responsible for the 

 late retraction of the umbilical vein for it is scarcely conceivable 

 that the contractile power of the degenerating musculature of 

 the vessel would itself be sufhcient to bring about this late 

 retraction. Indeed, the absence of the round ligament or um- 

 bilical vein in the region between the umbilicus and the tip of 

 the xiphoid process must be due to a comparatively rapid re- 

 traction and degeneration of the distal portion of the vein and 

 it is especially significant that no fibrous renmant can as a rule 

 l)e foimd between the umbilicus and the caudal extremity of the 

 umbilical vein of animals, which is at all comparable to the 

 fibrous remnants found between the umbilicus and the distal 

 extremities of the hypogastric arteries in man. According to 

 Robin, the adventitia of the arteries remains behind during the 

 ])rocess of the delayed retraction in man and if it were also left 

 behind in the later delayed retraction in non-ruminants one 

 could suppose that the fine, fibrous, filaments l)etween the 

 hypogastric arteries and the umbilicus, in man, might have 

 such an origin, but as will be seen later, such an assumption is 

 unnecessary. 



The rate of degeneration of the suspensoi-y ligament and es- 

 IK'cially of the umbilical vein, in cats seems to be determined 

 \ery largely by the previous existence or by the genesis of venous 

 radicles which j^our their })lood into its caudal extrennty. Such 

 a condition was noticed very commonly in cats and guinea-pigs 

 but never in dogs and sheep, although the degenerating umbil- 

 ical vein may rarely acquire a secondary attachment in these 

 animals also. It is a rather remarkable thing that after becom- 

 ing detached at the umbilicus, the retracted umbilical vein not 



