Textbook of normal histology: including an account of the development of the tissues and of the organs . l small groups of ganglion-cells occur within themuscular tissue associated with the fibres supplying the intimatestructure. The nerves and the blood-vessels are covered by thevisceral pericardium. The development of all parts of the circulatory apparatustakes place within the mesoderm; while possessing a commonorigin, the blood-vessels and the heart, however, develop in-dependently, and, for a time, are distinct and dis- FlG- I27- connected. The earliestblood-vessels appear nearthe periphe
Textbook of normal histology: including an account of the development of the tissues and of the organs . l small groups of ganglion-cells occur within themuscular tissue associated with the fibres supplying the intimatestructure. The nerves and the blood-vessels are covered by thevisceral pericardium. The development of all parts of the circulatory apparatustakes place within the mesoderm; while possessing a commonorigin, the blood-vessels and the heart, however, develop in-dependently, and, for a time, are distinct and dis- FlG- I27- connected. The earliestblood-vessels appear nearthe periphery of the vascu-lar area, outside the limitsof the proper body of theembryo ; later and second-arily they extend centrallyand unite with the primitiveheart and those parts of thelarge trunks which havebeen formed coincidentlywithin the embryo. The mesodermic elements within certain tracts near the peripheryof the vascular area undergo proliferation, which results in the pro-duction of deeply staining densely nucleated areas known as theblood-islands of Pander; these are the direct progenitors of the. Developing capillary blood-vessels within the omentumof young rabbit: a, a, elongated protoplasmic processesconnecting the walls of the newly-formed capillary (c)with the angioblastic connective-tissue corpuscles (b). lo< NORMAL HISTOLOGY. earliest blood-vessels and the first blood-cells. The blood-channelsappear within the nucleated islands as spaces which follow thepartial breaking down of the inner portions of the areas. Theperipheral zone of the nucleated cell-mass becomes the endotheliumof the future blood-vessel, while, probably, certain of the enclosedmesodermic elements persist as the primary blood-cells. After atime the mesoderm surrounding the newly-formed endothelial tubedifferentiates into the muscular and other tissue of the remainingcoats. The endothelium is, therefore, genetically the oldest partof the vessel, although its characteristic appearance, as seen insilv
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Keywords: ., bookauthorpiersolgeorgeageorgea, bookcentury1800, bookdecade1890
