518 ARTHUR WILLIAAl MEYER 



them always ran farther caudally and it was this one in which 

 blood could usually be seen. The other strand was shorter, firmer, 

 whiter and looked more like an artery. Upon microscopical 

 examination it was found that the single strand usually con- 

 tained two vessels one of which might have the characteristics 

 of a vein and the other that of an artery or they might be indis- 

 tinguishable. In case of the second isolated strand which ex- 

 tends farther caudally the only vessel contained in it looked like 

 a vein. Injection of these from the superior mesenteric vein, 

 in cats one week old was easily accomplished. 



Robin called attention to the presence of blood in the omphalo- 

 mesenteric vessels in cats forty-eight hours after birth, described 

 the course of the vessels and added that in some cats there might 

 be three instead of only two vascular strands each containing 

 two veins and two arteries. According to Robin the omphalo- 

 mesenteric vessels of the cat detach themselves at the end of 

 one month but as stated above, it is beyond question that not 

 infrequently these degenerating vessels can be found attached 

 to the umbilicus as late as six months and one year or more 

 after birth. 



Upon microscopical examination these undetached vessels 

 were usually found to have fairly well-preserved walls with a 

 distinct lumen. No elastica interna was observed and the 

 musculature whio-h had undergone regression was composed of 

 indistinct circularly disposed fibers only. A definite adventitia 

 was not present for it merged into the surrounding thick layer 

 of fibrous connective tissue which was enclosed by peritoneum 

 (fig. 26). The lumen was large, circular or elongated in cross 

 section and contained some well-preserved erythrocytes as a 

 rule. Each strand contained but a single large vessel and two 

 vessels in each strand as reported by Robin were never seen 

 except in regions where the two separate strands had joined. 

 In case of the presence of three strands three vessels would, of 

 course, be present here. 



The apparent failure of the omphalomesenteric vessels to be 

 c()mi)letely transformed into filirous cords before their complete 



