The cleft in his breast might close up now, and the last remnant of his yolk-sac vanish forever.
(a) The vitello-intestinal or omphalo-mesenteric duct and the yolk-sac or umbilical vesicle.
About the twelfth day the mouth-pit shows, and the gut-tract is partly separated from the yolk-sac.
The head and even the region of the pronephros are clearly separate from the yolk-sac; the mouth is coming to be formed.
The epiblast spreads uniformly over the yolk-sac and not on the one side only as in the former eggs.
The duodenum extends only a short distance caudad to this point and then opens, aip, to the yolk-sac.
In this thickened edge a circular vein arises, which brings back the blood from the yolk-sac to the embryo.
The digestive system is advanced to a gut-tract, which is a straight tube connected with the yolk-sac.
The yolk-sac is shown here simply as an irregular piece of tissue, the yolk having been removed.
At the margins of the germinal area these layers are of course continuous with the rest of yolk-sac wall.
yolk sac n.
A membranous sac attached to an embryo, enclosing food yolk. Also called umbilical vesicle.
|yolk sac |
A sac that is attached to the gut of an embryo and encloses the yolk in bony fish, sharks, reptiles, mammals, and birds. In most mammals, the yolk sac functions as part of the embryo's circulatory system before the placenta develops.