THEthreeUmbilical Vesselsconsist ofone VeinandTwo Arteries; which compose theNAVEL-STRING, and are wrap’d up in one strongMembrane, proceeding from theChorionandAmnion, between theNavelandPlacenta.
THEVeinarises in thePlacenta, from innumerable minuteVessels; proceeding thence withSpiral Contortionsbetween theArteries, thro’ theNAVEL-STRING,andNavel, to theLiverof theInfant; terminating in theSinusof theVena Porta, into which it pours theBloodandnutritious Juicereceived in thePlacenta; which immediately proceeds to theVena Cava, andHeart, thro’ aCylindrical Canal(call’dVenosus) opposite to theUmbilical Vein.
THEArteries, which are scarce half so large as theVein, arise from theIliacsof theInfant, or from theAorta. They pass both Sides of theBladderto theNavel, and thence through theNAVEL-STRING, by the likeSpiral Windings, to thePlacenta: where, after distributing someBranchesto theAmnionandChorion; they are divided into a very great Number ofSprigs, transferring theBloodfrom theFÅ“tusto theSECUNDINE.
THESETwo Arteries, with the above-mentionedone Vein, make up a certainPart, twisted like aRope, about one Inch thick, and near a Yard long, call’d theNAVEL-STRING; which is so ordained of thisLength, that theInfant, by itsMotion, may not pull thePlacentafrom theWomb; and that, by itsMeans, theSECUNDINEmay be commodiously extracted after theBirth.
INCase ofTwins, or moreChildren, every one has its properNAVEL-STRING; the chief Use of which is, to convey theMaternal Bloodandnutritious Juicesby theVeinsto theFoetus, for itsAliment: TheArteriescarrying back that which is unfit for thisUse, to thePlacenta; whilst theFœtusis still supply’d with more by theVein: So that there’s acontinual Circulation, or Communication, between theMotherand herInfant.