. Elementary biology, animal and human. Biology. A=Surface view, B=Longitudinal section. Fig. 36. — Structure of capillaries. occur. Hence, the capillaries form the most important portion of the blood system. 164. Structure of the capillaries. — In structure the capil- laries are extremely simple (Fig. 36). At the points in the blood system where arteries end and capillaries begin, muscular and elastic tissues are wanting. The walls of the capillaries are formed of a single layer of very thin- walled cells. We have in this arrangement the best possible conditions for the process of osmosis. On
. Elementary biology, animal and human. Biology. A=Surface view, B=Longitudinal section. Fig. 36. — Structure of capillaries. occur. Hence, the capillaries form the most important portion of the blood system. 164. Structure of the capillaries. — In structure the capil- laries are extremely simple (Fig. 36). At the points in the blood system where arteries end and capillaries begin, muscular and elastic tissues are wanting. The walls of the capillaries are formed of a single layer of very thin- walled cells. We have in this arrangement the best possible conditions for the process of osmosis. Only the thin membrane of the capillary wall separates the blood from the surrounding tissues, and an exchange of materials between the two is readily carried on. 165. Position of the veins. — On the back of the hand one sees through the skin a branch- ing system of bluish blood ves- sels. These are veins. Unlike the arteries, veins have no pulse. Many veins, like those in the hand, lie near the sur- face, while most of the arteries, as we have stated above, are -^ = '"^'"^ '"'^ open to show shape of , , _ , valves; B = section of vein showing valve buried deeply among the other open; C = section of vein showing valve ,. closing. tissues. 166. Structure of veins. — When the veins are emptied of blood, they immediately collapse. This is due to the fact. A B C Fig. 37. — Structure of a Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Peabody, James Edward, b. 1869; Hunt, Arthur Ellsworth, joint author. New York, The Macmillan company
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1912
