488 ARTHUR WILLIAM MEYER 



generates very rapidly. But in the cat, guinea-pig, rat and rabbit 

 in which the vein is not isolated and in which the suspensory- 

 ligament degenerates much slower, it occupies a relation similar to 

 that of the hypogastric arteries in the same animals. In these 

 animals it is also exceedingly common to find one or more small 

 veins running roughly parallel to and in the immediate vicinity 

 of the degenerating umbilical vein. The largest of these is usually 

 plainly'- visible to the naked eye but the rest are generally of micro- 

 scopic size only. Although injections of these vessels were not 

 made yet from observation with the unaided eye and from a study 

 of sections of the ligaments they apparently correspond to the 

 para-umbilical veins of Sappey rather than to the vein of Burow. 

 The largest of these veins which does not join the degenerating 

 umbilical vein is generally plainly visible because it is filled with 

 blood. In the dog there frequently are also a large number of 

 microscopic veins in the adventitia of the degenerating umbilical 

 vein which join the latter. These seem to be most numerous 

 at the distal extremity of the vessel where the lumen is frequently 

 multiple, and arise from the vasa vasorum. 



The behavior of the hypogastric arteries in these animals was 

 quite different from that of the vein for they retract quite early 

 and usually become attached to the apex of the bladder. They 

 had already retracted in young rats whose eyes had not yet 

 opened and could be traced peripherally only as far as the apex 

 of the bladder. In a rat approximately three months old no 

 trace of them could be found microscopically in this region. 

 In cats eleven to twelve days old they have usually begun to 

 retract although the urachus is often and the umbilical vein 

 is always, still attached to the umbilicus at this time. It is 

 also true, no doubt, that the time of separation of the arteries 

 is dependent upon the time of sloughing of the cord, which 

 undoubtedly varies as much in animals as Weckerling's ('08) 

 extensive analysis showed it does in the human infant. In a dog 

 one week old the vessels were still firmly attached and there was 

 no indication of a beginning retraction. These observations 

 confirm those of Robin although I cannot corroborate his ob- 

 servation that the retraction of the arteries is always simul- 



