THE LYMPHATICS. 



719 



Fig. 395. 



afferent and efferent vessels) that surrounds their proper substance, which is 

 composed of two layers of a different aspect — one cortical, the other medullary. 



The first appears to be granular, the second somewhat fibrous. This proper 

 tissue is sustained by connective laminse (or trabeculce. septa — continuations of 

 the capsule) which contain smooth muscular fibres. The trabeculge form alveoli 

 in the cortical layer, and a sort of minute tubes in the central layer. These 

 alveoli — or follicles — are in their turn divided by fine reticular connective 

 tissue into secondary spaces, which become smaller as they lie nearer the centre ; 

 at the periphery, where they are most 

 voluminous, they are named lymph sinuses. 

 Everywhere these sinuses are filled with 

 lymph corpuscles. The arrangement is 

 identical in the medullary substance; in the 

 interior are seen a great number of arterial 

 capillaries or lymphatic cords. The nerves 

 are derived from the sympathetic system. 



The afferent lymphatics, where they 

 ■enter the gland, communicate with the 

 alveoli in the cortical substance ; these 

 alveoli are connected by the cords of the 

 central layer, and the latter are united, 

 in their turn, to the alveoli of the op- 

 posite side of the cortical substance, from 

 which the efferent ramuscules spring. The 

 lymph, therefore, traverses every part of 

 the gland, and during this very tortuous 

 course becomes charged with lymph-cells. 



Certain glands have a much simpler 

 structure, being entirely composed of 

 lymphatic capillaries rolled up on them- 

 «elves in clusters, and anastomosing in 

 networks. These capillaries arise from 

 the divergent arborization of the afferent 

 vessels, and are continuous with the con- 

 vergent branches which, by their union, 

 form the efferent lymphatics. The organs 

 have received the name of fcdse ylctnds, 

 though they are really lymphatic glands. 

 In support of this assertion, it may be 

 said that " in descending the animal series, 

 we see the glands becoming more and 

 more simplified, and transformed at a 

 great number of points into an interlacing of vessels. In birds, they only occupy 

 the base of the neck and the entrance to the chest, forming in all the other 

 regions simple plexuses ; in reptiles and fishes, the lymphatic glands disappear 

 altogether, and the plexuses that replace them are themselves not at all compli- 

 cated" (Sappey). 



(The cortical part of the gland contains the round masses of adenoid tissue — 

 sometimes called secondary nodnles — which are continuous with the oval masses, 

 also adenoid tissue, found in the medullary portion ; and both oval and round 



PORTION OF THE MEDULLARY SUBSTANCE OP 

 THE MESENTERIC GLAND OF AN OX, THE 

 ARTERY OF WHICH IS INJECTED WITH 

 CHROMATE OF LEAD (MAGNIFIED 300 

 DIAMETERS). 



a, Medullary substance with capillary net- 

 work, fine reticulum of connective tissue, 

 and a few lymph corpuscles ; b, b, super- 

 ficial lymph-path, traversed by a reticulum 

 of nucleated cells (c, c), with numerous 

 anastomosing prolongations. The lymph 

 corpuscles have for the most part been 

 removed ; d, d, trabeculae composed almost 

 exclusively of unstriped muscular tissue ; 

 g, a small medullary cord, or bridge, con- 

 taining a blood-vessel and numerous lymph 

 corpuscles. 



