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(seq. 47)
20 Lect. 2
those of Trees do not N 13. In the Kidneys, however they do not anastomose - The largest Anastomosis is in the Basis of the Skull, made by the two Vertebrals, near the Foramen Occipitale. Small Branches of Arteries frequently anastomose, the Advantage accruing from this is, that the Blood is more thouroughly mixed, also an Equilibrium is kept up; if one Branch is obstructed, it passes thro' another, or if it is too full, goes to the collateral Branches - The other Advantage is, that when an Artery is destroyed for a Time, that Part may have its Nourishment by another, as in the Aneurism, when the great Artery of the Arm is mortefied divided, the Limb would mortify, were it not for these lateral Communications - There are said to be three Kinds of Arteries [?] Sanguiferous, Serous, & Lymphatic, according to Leuvenhoek's Doctrine, tho' the two former might be sufficient, as the last is only Theoretical - We have now a distinct System under the Name of Lymphatics - Boerhaave's Error Loci may be understood from hence, & is founded upon it, i. e. when serous Arteries are distended with red Globules. The Arteries begin in the Heart, & terminate in the extreme Branches - 1st The greatest Numbers terminate in Veins. - 2d. Some in Glands i. e. in secretory Vessels. 3d. Upon Surfaces, as on the spongy Surface of the Penis, where the Arteries open into the spongy Cells, & we believe, that the Perspiratory Vessels or Exhalents are Continuations of Arteries, tho' transudation may better account for the - Situation - The Arteries begin almost in
(seq. 49)
21 Lect. 2
the Center of the Body, & run nearly in the Center of each Limb, giving a Branch to every Part. In the Limbs, they lie, as near the Bones, as can be, & thus generally lie in an hollow Part, so as not to be much stretched or compressed, & commonly in the Bend of any Part. Mr. John Hunter observed, that Branches near the Heart, go off at right Angles, which in some Measure to lessen the Impetus of the Blood's Motion; & at a Dis- tance at Acute Angles, to quicken in some Measure the Velocity. Arteries in their March, in some places run serpentine or are convoluted, as in the Uterus, because of the greater Distension at different Times of Gestation according to Dr. Friends Observations. But Dr. Hunter thinks, that is not the Reason, for in the greatest Distintion the Artery is still more convoluted, which therfore is to answer some other Purpose.
There are Valves in the Arteries, but it is only from their Beginning, viz. in the Aorta & pulmonary Artery, which prevents the Return of the Blood back to the Heart. The Valves are generally made up of three folds or Membranes, but there are Instances only of two End of Lecture 4 [?] Lect 5 Feb 23 Anatomists have been accustomed to divide the Substance of the Body into different Layers, the Coats of the Arteries are said by some Authors to be stiffly partly muscular but they are manifestly not so in Colour, but they are made up of an elastic Ligamentous Substance of a particular Texture resembling white Leather, that is elastic both in longitudinal & Transverse
