266 



SCIENCE 



[N. S. Vol. XXXVII. No. 946 



Moreover, the distal extremity of the degenerating 

 umbilical vein after being freed from the abdom- 

 inal wall may obtain a secondary attachment as a 

 result of the formation of adhesions, to the 

 parietal peritoneum usually somewhat more cra- 

 nial to the umbilicus; to the liver or gall bladder; 

 or most commonly to the extensive fold of extra- 

 peritoneal fat lying ventrally in the median line 

 between the processus xiphoideus and the um- 

 bilicus. Besides, such secondary attachments — 

 which are, of course, purely temporary — may 

 nevertheless retard the progress of the degenerative 

 changes in the umbilical and omphalo mesenteric 

 veins considerably. This is especially well illus- 

 trated in case of the omphalo mesenteric veins of 

 the cat which are not rarely present still in cats 

 one to two years old because they have come into 

 more or less permanent relations to, and function 

 as part of the systemic venous system. This 

 rather surprising fact was especially well illus- 

 trated in two cats in which one of the omphalo 

 mesenteric veins had obtained a secondary attach- 

 ment to the apex of the bladder and arose iu 

 several vesicle veins. In these cases the omphalo 

 mesenteric vein was patent throughout, filled with 

 blood which could be forced into the superior 

 mesenteric vein very easily by pressure and which 

 was later expelled spontaneously by contraction 

 in response to cooling of the vessels after death. 

 A similar phenomenon was noticed in case of the 

 umbilical vein of the cat, the distal degenerated 

 and retracted extremity of which obtained a sim- 

 ilar connection with the extra-peritoneal veins of 

 the' ventral body wall. It is evident, of course, 

 that the establishment of such secondary vascular 

 connections on part of the umbilical vein might 

 and does materially affect the rate of regression, 

 not only of the vein itself, but of the suspensory 

 ligament as well. This is particularly true if, as 

 is not infrequently the case in cats, a very large 

 lymphatic vessel lying between the layers of the 

 suspensory ligament extends parallel to its con- 

 cave and free caudal border. 



The extremely late disappearance of the om- 

 phalo mesenteric vessels in the cat not uncom- 

 monly observed is as remarkable as the early 

 disappearance of the umbilical vein in the dog and 

 sheep. Indeed it is not rare to find the omphalo 

 mesenteric vessels persisting as fine fibrous strands 

 which may contain no remnant of the lumen and 

 which have obtained a secondary attachment else- 

 "where, in cats half a year to a year old. 



The umbilical arteries which retract intra-ab- 



dominally instantaneously at the time of rupture 

 of the cord in Bos taurus and Ovis aries were never 

 found to have secured such a secondary attach- 

 ment, but in Canis familiaris, Felw domestica, 

 Lepus cuniculus, Mus ra-ttus and Cavia cobaya, in 

 which they remain attached to the abdominal wall 

 at the umbilicus and become detached only one to 

 two weeks post natum, their free ends obtain a 

 firm secondary attachment to the apex of the 

 bladder in the majority of cases. Yet they were 

 never observed to come into relation to the sys- 

 temic arterial system with their free ends or their 

 degenerating trunks. 



The early complete disappearance of the um- 

 bilical vein of the dog and sheep was due to a 

 degeneration of its musculature and consequent 

 absorption. These degenerative processes which 

 in these animals were sometimes accompanied by 

 a certain amount of connective tissue invasion 

 never ended in the formation of a truly ligamen- 

 tous structure, however. In the eat, rabbit and 

 guinea-pig, on the contrary, such a transformation 

 into connective tissue of at least the distal portion 

 of the umbilical vein was not uncommon. 



In case of the umbilical arteries in any of these 

 animals two methods of transformation were ob- 

 served. The connective tissue which displaced the 

 musculature arose either of subintimal or adven- 

 titial origin. In the first ease it formed between 

 the intima and the elastica interna when present, 

 which was usually the case, while in the second 

 case it displaced and invaded the media from 

 without. However, since there is a great deal of 

 connective tissue between the fasciculi and con- 

 centric layers of muscle fibers of foetal vessels, 

 both these processes may also be accompanied by 

 proliferation of the inter-fascicular, intra-medial 

 connective tissue. Moreover, it is evident that 

 these processes may all be combined. Neverthe- 

 less, this was usually not the case and instances 

 were observed in which the musculature was 

 plainly degenerating and being displaced only 

 from within, for the outer layers were well pre- 

 served, while in other cases exactly the opposite 

 conditions were present. 



No evidence whatever for the origin of con- 

 nective tissue from endothelium was obtained 

 and the initiation of degeneration and transforma- 

 tion were apparently independent of thrombus 

 formation, but apparently not of the presence of 

 non-coagulated blood in the lumen of the vessel. 

 L. B. Walton (Kenyon College) : The Anatomy 



of the North American Land Planarians. 



