On the source and the course of the embryonic blood circulation during development in the warm-blooded Vertebralia / by W. Macdonald.

  • Macdonald, William, 1797-1875.
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: On the source and the course of the embryonic blood circulation during development in the warm-blooded Vertebralia / by W. Macdonald. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    as the first form of the sinus venosus, with only one outlet— the ductus veuosus—leading to the umbilicus, continued by the umbilical vein, and from thence on the blastoderm membrane to the sinus terminalis of the chorion, to be traced afterwards. This conical union of the lymph sac has two inlets, by which it receives the venae cava3 after the vence-cardinales. As soon as the punctum salieus or genital blood particle stimulates the contraction of the conical sac, it discliarges its yellow lymph contents down the ductus venosus and onwards to the chorion, when its cavity is at once refilled from the venre cavfe and cardinalis, which again stimulate the sac to contract. This occurs early in the second day of incuba- tion, and, being continued, the embryonic blood circulation is thus carried on and repeated during incubation till to- wards its close during the last week, when some preparation is being made for pulmonary respiration and circulation. This change is more rapidly completed in the chick in ovulo- ovi than in the human embryo. The chick, at the beginning of the third week of incuba- tion, having swung from across the long axis of the egg to lie in its long axis, the air space of the broad end now by the removal of the yolk and albumen filling the whole egg-shell not occupied by the chick, the change to the pulmonary respiration and blood circulation is at once effected without any risk of still-birth, as the chick is already lying in atmospheric air, and has been heard to chirp in its prison cell a day or two before it escapes the egg-shell. The circulation thus originated continues to be regularly per- formed in the same manner, till a preparation is required for the pulmonary circulation towards the end of incubation. Previous to the fourth day of incubation, the heart, which at first consisted of a simple conical sac, the sinus venosus, had appended to its base a ventricle still membranous and contractile, thus giving it greater force from its extended contractile membrane to propel the blood through the rapidly growing embryo. This membranous form is subsequently enclosed within muscular walls by the intro- duction of the muscular tissue among the fibres of the