506 ARTHUR AVILLIAM MEYER 



Pollot ('09) in the ductus arteriosus in which the retrogressive 

 changes were usually not accompanied by thromoses. 



Since the retrogressive changes in the umbilical vein of the 

 cat, rat, rabbit and guinea-pig are so much slower and take 

 place in direct relation to and not largely or wholly independent 

 of those in the suspensory ligament as is the case in the dog, a 

 somewhat different condition might be expected to exist. This 

 is the case for in these animals the vein persists much longer 

 throughout a portion of its extent, and not infrequently a fibrous 

 structure which may somewhat rightly be termed a ligament 

 is substituted for it (figs. 18, 19 and 20). However, as already 

 stated, so far as the vein retracts or degenerates completely it 

 is not replaced l:»y a fil^rous cord and hence the process of degener- 

 ation in this, the distal portions, is from all appearances identical, 

 as a rule, with that in the dog and the sheep. In the more proxi- 

 mal portion of the umbilical vein a roughly cylindrical cord 

 composed of loose vascular fibrous connective tissue of hyaline 

 appearance which is sometimes markedly canalized is often 

 found in cats, rabbits and guinea-pigs. In cats from eleven days 

 to one year old this thickening in the caudal border of the sus- 

 pensory ligament is usually due to the presence of a band of well- 

 preserved fibrous connective tissue in whose proximal or intra- 

 hepatic portion a vessel which can be recognized as remnant of 

 the umbilical vein is usually present (figs. 4, 5, 18, 21). But 

 in its distal — or hepatic — portion near the xiphoid process, no 

 such remnant can be detected as a rule in cats only six months 

 old and occasionally no trace whatever of the umbilical vein was 

 found in any portions of the caudal border of the suspensory 

 ligament examined in cats one year old (figs. 19, 20, 21, 22, 23). 

 Indeed, in one instance such was the case in a cat only six weeks 

 old and it is worthy of special notice in this connection that in 

 the specimens from these and still younger cats, eleven days 

 old, the picture was always that of a pure degeneration without 

 the least indication of an endothelial proliferation and that 

 in those instances where remnants of the lumen were found 

 the endothelium was one-layered and well-preserved in places. , 



