. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. DEVELOPMENT OF THE BLOOD-VESSELS 223 B£ 131,-4), producing arteries and veins, the rest of the network forming capillaries uniting these two sets of vessels, and, this process continu- ing, there are eventually differentiated a single vitelline artery and two vitelline veins (Fig. 131, B). In the human embryo the small size of the yolk-sac permits of the extension of the vascular area over its entire surface at an early period, and this condition has already been reached in the earliest stage
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. DEVELOPMENT OF THE BLOOD-VESSELS 223 B£ 131,-4), producing arteries and veins, the rest of the network forming capillaries uniting these two sets of vessels, and, this process continu- ing, there are eventually differentiated a single vitelline artery and two vitelline veins (Fig. 131, B). In the human embryo the small size of the yolk-sac permits of the extension of the vascular area over its entire surface at an early period, and this condition has already been reached in the earliest stages known and consequently no sinus termin- alis such as occurs in the rabbit is visible. Otherwise the conditions are probably similar to what has been described above, the first cir- culation developed being associated with the yolk-sac. It is to be noted that the capil- lary network of the area vasculosa consists of relatively wide anasto- mosing spaces whose endothelial lining rests directly upon the sub- stance islands (Fig. 130). In cer- tain of the embryonic organs, not- ably the liver, the metanephros and the heart, the network has a similar character, consisting of wide anastomosing spaces bounded by an endothelium which rests di- rectly, or almost so, upon the par- enchyma of the organ (the hepatic cylinders, the mesonephric tubules, or the cardiac muscle trabecular) (Figs. 132 and 190, B). To this form of capillary the term sinusoid has been applied (Minot), and it appears to be formed by the expan- sion of the wall of a previously existing blood-vessel, which thus moulds itself, as it were, over the parenchyma of the organ. The. Fig. 130.—Surface View of a Portion of the Area Vasculosa of a Chick. The vascular network is represented by the shaded portion. Bi, Blood- island; Si, substance-island.—(Disse.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these
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Keywords: ., bookautho, bookcentury1900, bookdecade1910, booksubjectembryology
