CHANGES IN FETAL VESSELS OF THE LIVER 517 



the death of the anunal as the vessel cooled, the blood was 

 slowly forced out into the superior mesenteric vein and the 

 vessel then appeared only as a fine whitish cord. From these 

 findings and from the similar behavior of the degenerating 

 umbilical vein in dogs and sheep in which it not infrequently 

 obtains a secondary attachment to the prominent fold of fat 

 between the xiphoid and uml)ilicus, it is not only evident that 

 the fine fibrous filaments frequently found in cats have such an 

 origin. Moreover, it is evident that their persistence after 

 birth is largely determined by the fact and more especially 

 by the fact that they not infrequently come into relation with 

 the sj^stemic veins. It is also possible that the constant traction 

 exerted upon them as a result of peristalsis in the contained 

 coils of intestines is of some significance in this connection. 

 Whenever they obtain connection with the peripheral veins the 

 original lumen is preserved for a considerably longer time and 

 may be wholly intact even after the musculature has become 

 clearly degenerated. It is also evident that the arteries must 

 undoubtedly- degenerate first or earlier at least, for it is incon- 

 ceivable that they could form jmrt of the systemic circulation 

 even if they obtained a peripheral attachment. That this is 

 true is shown abundantly by the fact that in every case the 

 persisting vessels containing blood were veins and not arteries. 

 Moreover, no one has descril^ed a similar relationship of the 

 hypogastric arteries which because of their large size and much 

 later disappearance might be assumed to establish such a re- 

 lationship far easier than the much smaller and far more function- 

 ally transient omphalomesenteric arteries. 



Strangely enough such fibrous strands were never noticed in 

 rabbits and no remnant of the omphalomesenteric vessels could 

 be found in young rabbits more than 12 days old, while in guinea- 

 ])igs they are usually present at the age of three months or more. 

 In the few newborn dogs examined not more than two strands of 

 omphalomesenteric vessels were found and these were often 

 twisted about each other so as to form a single strand which 

 could be separated, however, as far as the lymph nodes at the 

 root of the mesentery. If the two strands were distinct one of 



