DEVELOPMENT OF MAKSUPIALIA. 710 



traced along the back between the ununited elements of the 

 vertebral arches ; posterior to the umbilical cord there is a small 

 projecting penis, and behind that, on the same prominence, is the 

 anus. This foetus and its appendages were enveloped in a large 

 chorion, ib. i, puckered up into numerous folds, some of which 

 were insinuated between folds of the vascular lining membrane 



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of the uterus, but the greater portion was collected into a 

 wrinkled mass. The entire ovum was removed without any 

 opposition from a placenta! or villous adhesion to the uterus. 

 The chorion, fig. 567, , #, was extremely thin and lacerable, and 

 showed no trace of villi on the outer surface. The membrane, 

 ib. b., extending from the umbilicus to the inner surface of the 

 chorion, was highly vascular. The foetus was immediately enve- 

 loped in a transparent amnios. On turning the chorion away from 

 the foetus, it was found to adhere to the vascular membrane ; but 

 they could be separated from each other, without laceration, for 

 the extent of an inch ; at this distance from the umbilicus the 

 adhesion was closer : and here the umbilical membrane termi- 

 nated in a well-defined ridge, formed by the trunk of a blood- 

 vessel. ^Vhen spread out, as at b, b, fig. 569, its figure was that 

 of a cone, of which the apex was the umbilical cord, and the 

 base the ( vena terminalis.' Three vessels diverged from the um- 

 bilical cord and ramified over it. Two were continuations of 

 the terminal or marginal vein : the third was the arterial trunk. 

 The amnios, ib. c, was reflected from the umbilical cord, and 

 formed, as usual, the immediate investment of the foetus. 



The umbilical cord measured two lines in length and one in 



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diameter : besides the three vessels above-mentioned, it included 

 a small loop of intestine ; and from the extremity of the latter a 

 filamentary process was continued to the vascular membrane. On 

 tracing the contents of the cord into the abdomen, the two larger 



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vessels, filled with coagulated blood, were found to unite ; the 

 common trunk then passed backward beneath the duodenum, and 

 after being joined by the mesenteric vein, went to the under 

 surface of the liver, where it penetrated that viscus : this was con- 

 sequently an omphalo-mesenteric or vitelline vein. The artery 

 was a branch of the mesenteric. The membrane, therefore, upon 

 which they ramified answered to the vitellicle, i. e. the vascular 

 and mucous layers of the germinal membrane, which spreads 

 over the yolk in oviparous animals, and which constitutes the 

 so called 'umbilical vesicle' of the embryo of placental Mam- 

 malia. The filamentary pedicle which connected this membrane 

 to the intestine was given off near the end of the ileum. 



