Identifier: handbookofphysio00bake (find matches)
Title: Hand-book of physiology
Year: 1892 (1890s)
Authors: Baker, W. Morrant, (William Morrant), 1839-1896 Harris, Vincent Dormer Kirkes, William Senhouse, 1823-1864. Hand-book of physiology. 13th ed
Subjects: Physiology Human physiology
Publisher: London : John Murray
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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acquire red colour; these form the red blood-corpuscles. The proto-plasmicprocesses become hollowedout in the centre so as to forma closed system of branchingcanals, in the walls of whichthe rest of the nuclei remainimbedded. In the blood-ves-sels thus formed, the circula-tion of the embryonic bloodcommences. According to Klein, the firstblood-vessels in the chick aredeveloped from embryonic cellsof the mesoblast, which swellup and become vacuolated,while their nuclei undergosegmentation. These cellssend out protoplasmic pro-cesses, which unite with cor-responding ones from othercells, and become hollowed,give rise to the capillary wallcomposed of endothelial cells;the blood corpuscles being-budded off from the endothe-lial wall by a process of gem-mation. Heart. — About the sameearly period the heart makesits appearance as a solid massof cells of the splanchno-pleure in the manner beforeindicated. At this period the anteriorpart of the alimentary tubeends blindly beneath the noto-
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Fig. 489.—Capillary blood-vessels of the tailof a young larval frog, a, capillariespermeable to blood; b, fat granules at-tached to the walls of the vessels, andconcealing the nuclei; c, hollow prolon-gation of a capillary, ending in a point;d, a branching cell with nucleus and fat-granules ; it communicates by threebranches with prolongation of capillariesalready formed; e, e, blood corpusclesstill containing granules of fat. x 350times. (Kolliker.) chord. It is beneath theposterior end of this fore-gut that the heart begins to be developed.The heart when first formed is made up of two not quite completetubes which coalesce to form one, and so when the cavity ishollowed out in the mass of cells, the central cells float freely in CH. XIX.) BLOOD VESSELS. 821

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