CHYLIFEROUS SYSTEM (in Compa rative Anatomy) is that portion of the vascular system of vertebrated animals which is destined to convey the nutritious part of the food, or the chyle, from the alimentary canal into the san guiferous vessels. The function of these chy liferous vessels appears to be performed by the veins in the invertebrated classes, where the white colour of the blood causes them to re semble more closely the lacteals or chyliferous vessels of vertebrata. Several parts, however, of the invertebrated animals have been taken by anatomists for this lacteal system, as the .
nervous system of Mollusca by Poli, the tubuli of Insects by Sheldon, the mesenteric vessels of Echinodermata by Monro, the radi ating prolongations from the stomach of Me dus by Carus. The chyle of vertebrata, derived from the chyme of the digestive canal, and much resembling the white blood of the lower divisions of the Animal Kingdom, varies in its physical properties and chemical com position in the different tribes of animals, and in the same animal according to the kind of food on which it subsists, (see CHYLE') being most allied to red blood in the highest animals and those which subsist on the most nutritious animal food, and being most remote from that condition in the lowest fishes and the most imperfect animals. The vessels which con vey, and still further elaborate, this fluid,. the chyliferous system, like the other systems of the body, present very different grades of de velopment in the different classes of .vertebrata.
In fishes. they consist of simple vessels in which we cannot separate the two usual tunics; they are destitute of internal valves and me senteric glands, they form two strata of vessels between the coats of the small intestine, and they convey a limpid chyle to the,recepiaculum chyli, from which it is sent ,by one or two thoracic ducts to the branches of the su perior cava or the jugular veins. They com municate freely with the veins, they already present numerous constrictions as rudirinentary valves, they present valvular orifices at their entrances into the veins, and their numerous convoluted plexuses supply the place of me senteric glands.. .
. The chyliferous vessels are nearly in the same condition of development in the amphi bia, where they form two layers on the parietes of the alimentary, canal, are destitute of con globate glands form plexuses on the extended mesentery, and' terminate in two thoracic.ducts which proceed forwards along the sides of the vertebral column. (See AmPIIIBIA.) In the class of reptiles the lacteals pre sent a more advanced stage of formation, chiefly in the. development of the internal valves in the trunks and branches in all these animals, and in the white milky condition of their contents in the crocodilian family. (See REPTILIA.) They are still without mesenteric glands, their valves are less perfect than in birds and quadrupeds, and the chyle is still limpid and colourless in the serpents, lizards, and tortoises. The coarse vegetable food of the chelonia, and the great length of their small intestine, give occasion for the numerous large chyliferous vessels which cover their alimentary canal and mesentery. The place of mesenteric conglobate glands is yet supplied, as in the inferior vertebrata, by numerous complicated networks of lacteal vessels, formed in.different parts of their course; and, as in fishes, two or more ducts are here observed passing forwards from a single wide receptaculum. The tho mcic ducts form nunierous free anastomoses with each other in their course forwards to the neck, accompanying the left branch of the aorta to the anterior part of the trunk, where they pour the:r contents into the jugular or subclavian veins, or into the angle between these ,vessels. Before entering the veins these ducts receive the lymphatic trunks, as in other classes, from the head and arms. The chyli ferous vessels of the chelonia coining from the outer and inner layers spread on the small in testine, unite into considerable trunks, which pass along the mesentery in close proximity to. the bloodvessels. The thoracic duct of the tortoise surrounds and almost conceals the trunk of the aorta by its numerous large anas tomosing branches.