The elements of embryology (1874) The elements of embryology elementsofembryo01fost Year: 1874 D Fig. 8, ^4 to .2V forms a series of purely diagrammatic representations in- troduced to facilitate the comprehension of the manner in which the body of the embryo is formed, and of the various relations of the yolk-sac, amnion and allantois. In all vt is the vitelline membrane, placed, for convenience sake, at some distance from its contents, and represented as persisting in the later stages; in the actual egg it is in direct contact with the blastoderm (or yolk), and early ceases to have a separa
The elements of embryology (1874) The elements of embryology elementsofembryo01fost Year: 1874 D Fig. 8, ^4 to .2V forms a series of purely diagrammatic representations in- troduced to facilitate the comprehension of the manner in which the body of the embryo is formed, and of the various relations of the yolk-sac, amnion and allantois. In all vt is the vitelline membrane, placed, for convenience sake, at some distance from its contents, and represented as persisting in the later stages; in the actual egg it is in direct contact with the blastoderm (or yolk), and early ceases to have a separate existence. In all e indicates the embryo, pp the general pleuro-peiitoneal space, af the folds of the amnion, a the amnion proper, ae or ae the cavity holding the liquor amnii, al the allantois, a the alimentary canal, y or ys the yolk or yolk-sac. A, which may be considered as a vertical section taken longitudinally along the axis of the embryo, represents the relations of the parts of the egg at the time of the first appearance of the head-fold, seen on the right-hand side of the blastoderm e. The blastoderm is spreading both behind (to the left hand in the figure), and in front (to right hand) of the head-fold, its limits being indicated by the shading and thickening for a certain distance of the margin of the yolk y. As yet there is no fold on the left side of e correspond- ing to the head-fold on the right, while therefore the front limit of the embryo, as distinguished from the blastoderm, is marked out by the head-fold, there is at present no tail-fold, and therefore no hind limit. B is a vertical transverse section of the same period drawn for convenience sake on a larger scale (it should have been made flatter and less curved). It shews that the blastoderm (vertically shaded) is extending laterally as well as fore and aft, in fact in all directions; but there are no lateral folds, and there-
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