CHYLIFEROUS SYSTEM. 425 



mucous coat of the intestine, they appear more obvious, and 

 have more symmetry in their distribution. Their trunks 

 unite with those of the lymphatics, to form a more regular 

 receptaculum, from which two thoracic ducts, with fewer 

 inosculations, advance forwards to terminate by several open- 

 ings on each side of the neck, at the junction of the subcla- 

 vian and jugular veins. This duplicity of the thoracic duct, 

 so general in the lower vertebrata, is occasionally found as an 

 abnormal character in man, when they are observed to pro- 

 ceed upwards on each side of the aorta, to terminate one in 

 each of the subclavian veins. The lacteals, like the lympha- 

 tics, thus accompany or envelope the trunks of arteries, to 

 profit by their constant pulsations, in forwarding their con- 

 tents to the veins, and their common trunks terminate in the 

 subclavian or jugular veins, as the most convenient place 

 near the heart and the lungs, throughout the vertebrated 

 classes. 



The chyliferous, like the lymphatic system, is more isolated 

 from the sanguiferous in the mammalia than in the lower 

 classes, and it manifests a higher development in the more 

 sanguineous character of the chyle, in the increased number 

 and more elaborate structure of the vessels and their valves, 

 in the existence of mesenteric glands, and in the concentra- 

 tion or unity of the thoracic duct. The small semilunar folds 

 in the interior of the lacteals are now so numerous and com- 

 plete, as to check the passage of injections from trunks to 

 capillaries, and to assist in forwarding the chyle to the tho- 

 racic duct ; and the two membranes forming the parietes of 

 the vessels are now more obvious, and more easily separated. 

 The more simple mesenteric plexuses of inferior classes, now 

 form small condensed conglomerate masses of minute capil- 

 lary lacteals, interwoven with capillary bloodvessels, so as to 

 form distinct, firm, red-coloured, rounded bodies, enclosed in 

 distinct tunics, and termed conglobate or mesenteric glands, 

 which present a great diversity in their size, their numbers, 

 and their degrees of approximation to each other, in the 

 different orders of quadrupeds. The lacteals and chyliferous 

 glands are almost confined to the small intestine in the 

 inferior vertebrata; but as the colon is more extended 

 in the mammalia, they are now found also, though in 

 smaller proportion, on the mesocolon. The receptaculum 



