IN Case of TWINS, or more _Children_, if conceived at _one Time_, they have but _one common SECUNDINE_, (notwithstanding the contrary Opinion of _others_) which adheres to the _Fund_ of the WOMB, by the _Placenta_, as above: Wherefore I must needs reject the _Testimony_ of such MIDWIVES, who give out that they have found the _SECUNDINE_, _fix’d_ to any _other Part_ of the WOMB; tho’ I experimentally know, that it is sometimes found in the _Hinder Part_ near the LOINS, sometimes in the _Forepart_, sometimes near the _Diaphragma_, sometimes in the _Right_, and sometimes in the _Left Side_. BUT however, we should be grossly mistaken, if from hence, we did conclude, that the _SECUNDINE_ adher’d to _any other Part_, than the _Bottom_ of the WOMB: Since such erroneous _Apprehensions_ are merely occasion’d by the various _Motion_, or oblique _Position_ of the WOMB; as hereafter will appear more at large. [Illustration] CHAP. XIII. _Of the UMBILICAL VESSELS, or NAVEL-STRING._ THE three _Umbilical Vessels_ consist of _one Vein_ and _Two Arteries_; which compose the _NAVEL-STRING_, and are wrap’d up in one strong _Membrane_, proceeding from the CHORION and AMNION, between the _Navel_ and _Placenta_. THE _Vein_ arises in the _Placenta_, from innumerable minute _Vessels_; proceeding thence with _Spiral Contortions_ between the _Arteries_, thro’ the _NAVEL-STRING_, and _Navel_, to the _Liver_ of the _Infant_; terminating in the _Sinus_ of the _Vena Porta_, into which it pours the _Blood_ and _nutritious Juice_ received in the _Placenta_; which immediately proceeds to the _Vena Cava_, and _Heart_, thro’ a _Cylindrical Canal_ (call’d VENOSUS) opposite to the _Umbilical Vein_. THE _Arteries_, which are scarce half so large as the _Vein_, arise from the ILIACS of the _Infant_, or from the AORTA. They pass both Sides of the _Bladder_ to the _Navel_, and thence through the _NAVEL-STRING_, by the like _Spiral Windings_, to the _Placenta_: where, after distributing some _Branches_ to the AMNION and CHORION; they are divided into a very great Number of _Sprigs_, transferring the _Blood_ from the _Fœtus_ to the _SECUNDINE_. THESE _Two Arteries_, with the above-mentioned _one Vein_, make up a certain _Part_, twisted like a _Rope_, about one Inch thick, and near a Yard long, call’d the _NAVEL-STRING_; which is so ordained of this _Length_, that the _Infant_, by its _Motion_, may not pull the _Placenta_ from the WOMB; and that, by its _Means_, the _SECUNDINE_ may be commodiously extracted after the _Birth_.