What is the Structure of the Veins?
The Veins are long and round Canals made of four kinds of Tunicks or Membranes, whose Office it is to receive the Blood that remains after the Nourishment is taken, and to carry it back to the Heart to be reviv'd.
What is the Form of the four Tunicks that make the Canals of the Veins?
The first is a Contexture of Nervous and streight Fibres. The second is a Plexus of small Vessels that carry the Nourishment. The third is all over beset with Glandules thro' which are filtrated the serous Particles of the Blood contain'd in the Vessels of the second Tunicle. The fourth is a Series of Annular and Musculous or Fleshy Fibres.
Which are the most numerous, the Arteries or the Veins?
The Number of the Veins exceeds that of the Arteries; and there are scarce any Arteries without Veins accompanying them.
Where is the Beginning and Original of all the Veins?
All the Veins have their Root in the Liver, and two of the three great Trunks that proceed from thence, are call'd Vena Portæ, and Vena Cava; and the third is twofold, viz. the ascending and the descending.
The Vena Portæ is distributed to all the Parts contain'd in the lower Belly, and terminated in the Fundament; where it makes the Internal Hæmorrhoidal Veins.