The anatomy of humane bodies with figures drawn after the life by some of the best masters in Europe and curiously engraven in one hundred and fourteen copper plates : illustrated with large explications containing many new anatomical discoveries and chirurgical observations : to which is added an introduction explaining the animal œconomy : with a copious index / by William Cowper.

Fig. 6.

A B C, The Inner and Smooth Surface of the Third or most In∣ternal Coat of the Artery; where the Foramina for the Branches which arise out of it, are exprest, and its Fibres extended according to its length B, C. The great Trunks of the Arteries do evidently appear to consist of a greater Number of Strata of Fibres, than those of the Veins; but the farther they recede from the Heart, they are both still more and more subdivided, and their Trunks and Capillary Branches become still thinner and thinner, till their outmost Extremities con∣sist of one single transparent Membrane; chiefly composed of such Tubes, as only convey their Succus Nutritius. And this I am apt to think may serve for the Description of Blood-Vessels in general; and shall farther consider the Organization of the several Extremities of the Blood-Vessels, in speaking of their particular Offices relating to Se∣cretion in the several Parts; wherefore at present shall only men∣tion, that the Extremities of Veins and Arteries are continued Chan∣nels, variously contorted and not all of them of an equal Size, even in Parts which are uniform or the same. Vid. App. Fig. 4.5.

After the Blood has past the Extremities of its Vessels, and is in its Return to the Heart again by the Veins; it there meets with divers Valves or Stops, which prevent the Weight of the Blood of the In∣ferior Parts of the Body, and the Recoiling of it in the Superior, (when any violent Motions affect the Thorax, as in Coughing, from pressing on the Extremities of the Vessels, and hindering its progressive Motion. That there is a Recoiling of the Blood in any extraordinary Motions of the Thorax, in the Jugular Veins, may be observ'd in taking Blood from thence, especially in Children. Hence it is the Valves in those Veins are necessary; least the Blood should again repass into the Vessels of the Brain with great Violence; which is also prevented in the Contortion made in the Internal Jugular Vein, in its Specus in the Basis of the Skull. I must confess I never yet observed above Two Valves (one opposite to the other) in the largest Vein that is fur∣nished with Valves; however Anatomists commonly mention Three, and Professor Bidloo tells us of Four and Five Valves, as they ap∣pear in the following Figures.