508 ANATOMY OF VERTEBRATES. 



close the vessel, the inner surface of which is shown at a : in B 

 the folds were continuous forming a subcircular valve, and con- 

 tained both fibrous and serous tissues : in c, besides the ordinary 

 pair of semilunar valves, b, b, there was a subcircular fold, c. 



343. Absorbent ganglions. These bodies, also called lympha- 

 tic or lacteal ' conglobate glands,' are much more numerous in 

 Mammals than in other Vertebrates. In the limbs they are 

 chiefly situated at the flexures of the joints ; and, being connected 

 by a looser tissue to surrounding parts, elude pressure by the 

 freedom of motion so allowed. They occur in the neck and head 

 external to the cranial cavity : in the thorax at the anterior and 

 posterior f mediastina,' and at the bronchial trunks where they 

 are usually discoloured by black carbonaceous matter. In the 

 abdomen they are found in the mesentery, near the spleen, and 

 along the side of the aorta, post-caval, and iliac vessels. In the 

 neighbourhood of the liver and gall-bladder post-mortem exudation 

 tinges them yellow : as a rule, they are of a pinkish grey tint. 

 The absorbents which enter the gland, fig. 397, B, a, , are com- 

 monly smaller and more numerous than those that quit it, ib. 

 e : the former, or ' vasa inferentia ' divide into small branches 

 previous to entering. They then finely ramify, lose their proper 

 tunics, and become continuous with those lacunar channels or 

 ' vacuoles ' which appear in the cell-mass of the developing 

 glands. 1 The preponderance of the fibrous tissue left, as it were, 

 in the peripheral part of the gland gives ground for the distinction 

 of a f cortical ' from a ( central ' portion. But there is no definite 

 boundary-line : septa extend from the ' cavernous ' capsule, at 

 first lamelliform in the cortical part and becoming cord-like or 

 1 trabecular ' in the central part. In the latter, the lymph- 

 channels become larger, especially in the mesenteric glands, and 

 have been termed { loculi : ' they are large in the mesenteric 

 glands of the Cetacea, though not in the degree, or with the 

 anatomical relations, described in CLXXIV", p. 27. They are 

 paved by the flat nucleate cells, and usually contain a whitish 

 pulpy matter : minute plexiform vessels, surrounding the ' loculi,' 

 form the beginnings of most of the ' vasa efferentia,' ib. e ; a few 

 are direct continuations of the inferent vessels. 



344. Disposition of Lymphatic s.--l.\\ the Mammalian class 

 the anatomical disposition of the lymphatic system has been 

 most completely traced out in the human subject. Success- 

 fully injected, the superficial lymphatics of the lower limb 

 present the general arrangement shown on the fore-part of 



1 CLXXVI". p. 152, 



