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(seq. 71)
32 Lect 2
Part digested off, besides the Danger of the Morti- fication spreading, & thus defeating the End of Amputation.
End of Lect. 5th 1784
Lect. 6th Feb 22 1784
Lect. 3. Of the Veins.
Veins have a great Analogy to the Arteries, being ramefying Tubes similar & of the same elastic Substance, only Thinner. What has been said of Arteries may be said of Veins, as to their Anastomosing, Branching, Course &c. Veins have Arteries for their Nourishment, as Arteries themselves have, called Arteriae Venarum. In the Stomach & Intestines the Arteries & Veins give off Branches together. Veins have nearly the same Quantity of Blood to carry, as Arteries, but are larger, otherwise, as they have thinner Coats, they would be more liable to be dilated by the Motion of the Blood, which from that Cause is slower in them. In the Veins the Circulation is quicker, as it comes nearer the Heart, for the same Reason a mentioned in the Arteries, viz because the Trunk there is smaller than all it's Branches - All Veins terminate in the Heart except one, viz the Vena Portarum, which terminates in the Liver. The Beginning of the Veins Physiologically is at the Branches, but Anatomically at the Heart. The Veins are 7 in Number viz 4 Pulmonary, 2 Vena Cava, & one Vena Portarum.
The Beginning of these were not known till before Injections & Microscopes brought them to Light. An Artery continued on
(seq. 73)
33 Lect. 3d
makes a Vein, or is a reflected Artery with some Irregularity, if we Inject by an Artery, it returns by the Vein. Quicksilver thus passing to the Veins does not prove a Continuation, but a Communication, for it might be carried into a Cell & be taken up by the Veins, but Muschenbrooke proves it. A Preparation of the Pia Mater injected with Tallow & Vermilion will shew it, as the Vermilion will often stand in the Arteries, & the Tallow return colourless by ye Veins. A Hand being injected with Quicksilver thro' the Artery the Quicksilver will return by the Veins very minutely by a good Preparation - Veins are divided by some Anatomists in the same Manner as Arteries viz into Sanguinaryferous, Serous & Lymphatic. But the Lymphatics are now known to be a distinct System. The General Distribution is the same, but is different in the Extremities, as deep seated with Arteries, & superficial without Arteries - In the Arms, there are two deep seated with Arteries & many Cutaneous ones also in the lower Extremities. The reason of this is probably from strong muscular Motion being used in the Arms, it would prevent the free Return of the Blood, but these Cutaneous ones help to take off this Impediment. And we see, if we clench the Fist, that the superficial Veins fill hence the Reason, why in Blood Letting it is necessary generally to make the Patient put his Hand in that Position.
(seq. 75)
34 Lect 3d
There are Veins, which are supposed to begin from the Internal Surface of Cavities, as in the Penis, [?] Anatomists suppose to prevail generally, but it is to be questioned, whether this is a fact. But the Absorbent Veins are demonstrable such as the Lymphatics. Veins are furnished with Valves - The Valves are made up of two loose Skins or Membranes, joining with their Edges, & sometimes of three, especially in larger Animals, as Horses &c. These prevent the Return of the Blood. The Valve makes a little Knot on the Veins. In the Human Body, The Valves of the Veins are in Pairs, the general Use is to prevent the Blood's returning back. Valves are not in all Veins, there are none in those of the Viscera, of the Brain, Lungs &c. They are found in the Extremities chiefly. It has been said, that as our Arms & Legs are more generally in a perpendicular Posture, & that if it were not for the Valves, the Pressure of the Column above would retard the Circulation; but this does not seem to be the Reason, as the Iliacs have none, but rather that the Circulation might be quickened by muscular Motion. As we find the more violent Exercise, We use, & the greater our muscular Motion, the quicker is our Circulation, & as the Bellies of Muscles swell in Contraction the Blood would be compressed in the Vein both forwards & backwards, whereas now the Valves hinder its returning