A-H

A-H

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1809 edition. Excerpt: ...occasion hereafter to apply. VVe shall conclude this article with some more particular account of the circulation through the brain than the pages of Dr. Motherby and his associate have supplied. To connect the whole, a little repetition is unavoidable. The course of the carotid arteries has been already explained; and the peculiarity in the circulation chiefly relates to the venous system. The veins are large and tortuous, unconnected with cellular substance, without valves; freely anzistomosing, and terminating in reservoirs rather than in large trunks. The apparent great object of this apparatus is to confine a certain portion of blood in the head; and, at the risk of a morbid accumulation, to prevent the source of the nerves from wanting at any time a supply. Even respiration, as we shall find, contributes to the same purpose. The mode in which the veins open into the sinuses confirm the same principle. We are informed byVicq d'Azyr that they open in a direction opposite to the current of blood; and, though the universality of this distribution has been doubted, it is admitted that they very frequently penetrate obliquely through the com; ofthe sinus, as the meters into the bladder; or that little valves occasionally cover their at eitures; a structure which produces the same effects.-Where the veins penetrate the dura mater, this membrane and the pia mater are united bya fatty substance, which has been mistaken for the glands of Pacconius; but these are in the cavity of the longitudinal sinus, and act still further as valves, to save the arteries from the danger of being exhausted; since these glands are placed at the entrance of the vein into the sinus. The course of the smaller veins is circuitous, and with difficulty explained...show more

Product details

  • Paperback | 826 pages
  • 189 x 246 x 42mm | 1,447g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236887980
  • 9781236887986