On the development of the vascular system in the foetus of vertebrated animals. Part II. / [Allen Thomson].

  • Allen Thomson
Date:
1831]
Catalogue details

Licence: Public Domain Mark

Credit: On the development of the vascular system in the foetus of vertebrated animals. Part II. / [Allen Thomson]. Source: Wellcome Collection.

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    days^ the whole of the finny part of the tail is covered by beauti¬ ful and minute arteries and veins. The loop of vessel when short and newly formed, has at first more the appearance of artery than vein, as the blood passes through it in jerks : as the loop elongates, however, and new branches proceed from it, the blood moves in jerks only in that part of the loop which com¬ municates with the arterial trunk, while in the part connected with the returning vein, the motion of the stream of blood be¬ comes uniform. Rusconi * has shewn very beautifully, that vessels are thus looped out during the development of the gills of the aquatic salamander. I find that nearly the same appearances present themselves in the gills of the frog, as well as in the extremities of the salamander. The anterior extremities of the salamander, when they first begin to sprout, form two small tubercles situa¬ ted behind the head, altogether destitute of circulating blood. Shortly after the appearance of these tubercles, a single vessel is seen winding round their extremities, which returns to the body without giving off any branches. The parenchyma of each of the toes, as it buds out from the end of the limb, receives a small loop from the original vessel. Communicating branches are likewise thrown across at the joints, and, as the limb becomes larger, numerous capillary vessels are formed in the same way as the primitive trunks. Spallanzani, and some other observers, have noticed similar appearances in the extremities of the chick, when they begin to be formed ; and the same may be seen in those of the rab¬ bit, and of some other mammiferous animals; from which there appears every reason to believe that, after the circulation of the blood has commenced, the development of new vessels from those already formed, takes place principally by means of loops in Warm as well as in Cold blooded animals. I ought now, in conformity with the plan previously laid down, to proceed to treat of the development of the individual parts of the vascular system in vertebrated animals ; but it must appear obvious, that a detailed account of the development of • Amours des Salamandres Aquatiques, et d^veloppement, &c. See Plate II. Figs. 8, 9, 10, 13, H h.