. Quain's elements of anatomy . itive blood and blood-vessels of the vascular area originate. The latter view is one which has long been advocated by various especially by His (No. 29 and No. Ill, i. and ii.), who in 1868 described theorigin of the vascular as well as the connective tissues as taking place in the lowerlayer, and forming a special part of the mesoblastic elements under the name ofjiarailastic. Similar views as regards the origin of the blood and vessels fromperipheral blastodermic elements were brought forward by Peremeschko andmaintained by Strieker and othe
. Quain's elements of anatomy . itive blood and blood-vessels of the vascular area originate. The latter view is one which has long been advocated by various especially by His (No. 29 and No. Ill, i. and ii.), who in 1868 described theorigin of the vascular as well as the connective tissues as taking place in the lowerlayer, and forming a special part of the mesoblastic elements under the name ofjiarailastic. Similar views as regards the origin of the blood and vessels fromperipheral blastodermic elements were brought forward by Peremeschko andmaintained by Strieker and others of the Vienna school (Nos. 91 and 93). In mammals the vesicular form of blastoderm, which results from thei ORIGm OF THE LAYEES. 755 holoblastic segmentation of the ovum, seems to determine some modifi-cation in the mode of formation of the layers. As ah-eady stated, thecompletion of the primary segmentation leads to the covering in of thewhole ovum with a layer of flattened nucleated cells, within which. Fig. 645. Fig. Fig. 645.—Embryonic area from the ovtrji op a rabbit op seven days. Y- (Fi-om KoUiker.) 2n\ first rudiment of the primitive strecak. Fig. 646.—Embryonic area from the ovum of a rabbit of eight days. y. (From Kolliker.) arc/, border of the embiyonic area ; pr, primitive streak with groove. besides the fluid remains of the original yolk-substance, there is theinner mass of granular cells or segmental sijheres, which by their furtherdevelopment and extension come to produce one or more deep or internallayers, which gradually spreading over the interior give a bilaminar ortrilaminar structure to an increasing area of the blastoderm. Kg. 64r.
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