▼OL. LTII.] PHILOSOPHICAL TRANSACTIONS. 365 



or right iliac, through that side of the pelvis; g the iliac veins going off to right 

 and left as usual; h the orifice of the umbilical vein, being so exactly of the 

 same diameter, of the same white colour and strength, and of the same con- 

 sistence with the divided trunk e, that at first sight, he took, this for the same 

 vessel. The trunk d was much thinner, and of a more bluish tint. 



Under the umbilical vein, was the umbilical artery on each side, which went as 

 usual into the pelvis, and there sent off the ordinary ramifications. On the 

 right side, its anastomosis with the iliac artery was very discernible; but on the 

 left he could not discover the iliac, a vessel which is pretty considerable, even in the 

 foetus, and was so on the other side, as seen at letter i. On the left side, the 

 umbilical artery, at its origin, or its inflection, had a kind of web of arteries 

 subdivided, some of which doubtless communicated with the aorta, or right iliac; 

 but neither of these branches appeared to be near the size of the right iliac, nor 

 could he find any thing like to the trunk, which he long suspected to be the 

 trunk of the right iliac; what vessels then are these trunks, d, e? Which of the 

 2 is the continuation of the umbilical, h ? This is a very important point, but 

 not easily determined. It would not have proved so, if he had injected the 

 umbilical vein, as he generally did in all his monsters ; or if he had taken more 

 care of the parts about the kidney-liver, which he certainly should have done, 

 had he but suspected so many singularities. 



He said, that at first sight, he took the trunk e to belong to the umbilical vein, 

 and it was still an opinion to which he was inclined, for the following reasons: — 

 ]. At this part e, the aorta had its greatest circumference; and, in tracing it 

 from this trunk, above as well as below, it grew less and less. This was, there- 

 fore, its trunk, or origin, and could not be a branch of it. 2. He had already said, 

 that the mouths, h, of the umbilical vein, and e, of the aorta inferior, were 

 exactly of the same diameter, of the same white colour, and of the same strength ; 

 and that the other vessel d was much weaker, of a laxer texture, and of a some- 

 what livid colour, like the coats of the veins. 



The umbilical vein is, with respect to the mother, or to the placenta, which 

 transmits the blood to the foetus, a real artery, going from the centre to the cir- 

 cumference, or from the principal body, which is the mother, to an adjoining 

 organ, which is the child ; and the umbilical arteries are properly veins, which 

 return the blood from that adjoining body to the common centre of the grand 

 circulation. The blood from the umbilical vein then is truly an arterial blood to 

 the foetus. In the usual structure of the embryo, nature has shortened all the 

 ways, to bring the arterial blood of the mother more speedily into the heart, into 

 the very aorta inferior of her foetus. Therefore, in a subject where there is no 

 heart, or even liver, that vein ought to communicate immediately with the aorta 



