. Elementary text-book of zoology. Zoology. LYMPHATIC SYSTEM. 67 in the Crocodilia, and in these animals the right aortic arch arises from the left ventricle. But the separation of the arterial and venous blood is even now not quite complete, for at the point where the two aortic arches cross one another there is a passage (foramen Panizza?) leading from one into the other, and through which a communication may take place. It is only in Birds and Mammals, in which, as in the Crocodilia, the right and left ventricle are completely separated, that a separation between the two kinds of blood is c
. Elementary text-book of zoology. Zoology. LYMPHATIC SYSTEM. 67 in the Crocodilia, and in these animals the right aortic arch arises from the left ventricle. But the separation of the arterial and venous blood is even now not quite complete, for at the point where the two aortic arches cross one another there is a passage (foramen Panizza?) leading from one into the other, and through which a communication may take place. It is only in Birds and Mammals, in which, as in the Crocodilia, the right and left ventricle are completely separated, that a separation between the two kinds of blood is completely effected (fig. 61). In Birds the right aortic arch persists, and the left entirely disappears ; while in Mammalia the opposite obtains, the left arch per- sisting and giving rise to the dorsal aorta. In these animals the blood is essentially diffe- rent from the chyle both in colour and composition, and there is present a special system of chyle and lymph vessels. This system origi- nates in simple tissue spaces, which are without walls, and its main trunks open into the vascular system. The con- tents are derived from the nutrient material absorbed from the intestine (chyle), and from the fluids which have transuded into the tissues from the capillaries (lymph), and they serve to renovate the blood. In the actual course of the lymph and chyle, , in the lymphatic vessels themselves, are placed peculiar glandular organs, known as lymphatic glands (blood glands), in which the lymph receives its form elements (lymph corpuscles=white blood corpuscles). Organs of Respiration. The blood needs for the retention of its properties not only this continued renovation by the addition of nutrient fluids, but also the constant introduction of oxygen, with the reception of which is clofely connected the excretion of cai'bonic. A Fir:. GO.—Heart and great vessels of a Cheloniim. Ad, right auricle ; As,left auricle; right aortic arch; , left aortic arch ; Ao, aorni; C
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
