CHYLIFEROUS SYSTEM. 



601 



nervous system of Molluscaby Poll, the biliary 

 tubuli of Insects by Sheldon, the mesenteric 

 vessels of Echinodermata by Monro, the radi- 

 ating prolongations from the stomach of Me- 

 dusae 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 receplaculum 

 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 rudimentary 

 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 AMPHIBIA.) 



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- 

 racic ducts form numerous 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 

 VOL. i. 



they pour their 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 coming 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. 



The inferiority of the chyliferous system 

 of birds to that of quadrupeds is seen even 

 in the properties of the chyle, which is still, 

 as in the lower tribes of vertebrata, a thin, 

 colourless, and limpid fluid. The lacteal ves- 

 sels are now, however, more obvious, and 

 more regular in their distribution, and are 

 spread in more crowded layers above the mu- 

 cous and above the muscular coats of the in- 

 testine. They collect from the intestine and 

 form numerous anastomosing plexuses on the 

 mesentery, in place of the conglobate glands 

 of mammalia, and then proceed, with the lym- 

 phatics, to the receptaculum, which sends for- 

 ward two thoracic ducts to terminate, on each 

 side of the neck, at the junction of the sub- 

 clavian with the jugular veins. (See AVES.) 

 The coats of the lacteals are still very thin and 

 distensible in birds; their valves, which are 

 more abundant on the trunks and branches 

 than in reptiles, are still so incomplete as to 

 allow injections to pass easily against their 

 course, and although conglobate glands are 

 not yet developed on the chyliferous system, 

 they are already perceptible on the lymphatics, 

 especially in the neck. 



The chyliferous system of the mammalia, 

 though more developed than that of all the 

 inferior classes, is still imperfect as a hy- 

 draulic apparatus when compared with the 

 sanguiferous system. The lacteal and lym- 

 phatic systems may still be regarded as mere 

 appendices of the venous, performing the func- 

 tions which are assigned to veins in the inver- 

 tebrated classes, and serving as inlets to the 

 materials which renovate the blood. No pul- 

 sating sacs have yet been detected in the lym- 

 phatic system of quadrupeds, nor any distinct 

 motion in the lacteals, the receptaculum, or 

 the thoracic duct. The chyliferous system of 

 this class presents a superiority of develop- 

 ment in the almost sanguineous characters of 

 the chyle, in the more perfect structure of the 

 vessels and their valves, in the development 

 of the conglobate mesenteric glands, in the 

 frequent unity or concentration of the thoracic 

 duct, and in the more isolated condition of this 

 system from the sanguiferous. The mesenteric 

 glands are chiefly confined to the mesentery of 

 the small intestine ; they are generally placed 

 apart from each other ; sometimes they are 

 united into a pancreas Asellii ; they are firm in 

 texture, highly vascular, and composed of con- 

 voluted lacteals, like more concentrated forms 

 of the plexuses of the lower vertebrata. 



(R. E. Grant.) 

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