520 ARTHUR WILLIAM MEYER 



SX\MMARY AND CONCLUSIONS 



1. The umbilical arteries of ruminants very likely rupture 

 extra-abdominally but at points which were intra-abdominal 

 previous to traction. 



2. Complete and immediate contraction of the arteries and 

 of the extra-abdominal portions of the veins is made possible 

 by the semi-fluid consistency of Wharton's jelly in these animals. 



3. The suspensory and round ligaments of the liver are purely 

 fetal structures in both the dog and the sheep. They degenerate 

 very early in life and a true round ligament never exists in them. 



4. Portions of both of these structures persist somewhat 

 longer in cats rabbits, and especially in guinea-pigs and rats in 

 which a more or less permanent round ligament is formed but 

 neither ligament was ever seen in old cats and rabbits. 



5. Degeneration and disappearance of the umbilical vein 

 proceed centripetally and remnants of the original lumen are not 

 necessarily preserved in the more or less temporary round liga- 

 ment which may be formed in some of these animals. 



6. The omphalomesenteric veins persist for an unusually 

 long time after birth, especially in cats and they and the de- 

 generating umbilical vein — except in the dog and sheep — may 

 come into relation to the peripheral venous system. In case of 

 the omphalomesenteric veins the establishment of this relation- 

 ship is always preceded by detachment at the umbilicus and 

 secondary attachment elsewhere. The detached degenerating 

 umbilical vein of the dog and sheep may also obtain such an 

 attachment but it never comes into similar relationship with the 

 peripheral venous system. 



7. No thickening or proliferation of the endothelium of the 

 intima was observed in the umbilical and omphalomesenteric 

 veins or in the hypogastric arteries of any of these animals and 

 thrombosis was not a factor in the process of obliteration. 



8. Fibrous transformation of the hypogastric arteries is due 

 to degeneration of the media accompanied or followed by an 

 ingrowth of connective tissue which is directly continuous with 

 the pre-ex' sting, sub-intimal, intra-medial or adventitial con- 

 nective tissue. 



