GENERAL CONSIDEEATIONS. 



Fig. 298. 



in the medullary substance ; in the interior are seen a great number of 

 arterial capillaries. The nerves are derived from the sympathetic system. 



The afferent lymphatics, where they enter the gland, communicate with 

 the alveoli which correspond to 

 the cortical substance ; these al- 

 veoli are connected by the cords 

 of the central layer, and the latter 

 are united, in their turn, to the 

 alveoli of the opposite 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 solid particles. 



Certain glands have a much 

 more simple structure, being en- 

 tirely composed of lymphatic capil- 

 laries rolled up on themselves in 

 clusters, and anastomosing in net- 

 works. These capillaries arise 

 from the divergent arborisation of 

 the afferent vessels, and are contin- 

 uous with the convergent branches 

 which, by their union, form the 

 efferent lymphatics. The organs 

 have received the name of false 

 glands, though they are really 

 lymphatic glands. In support of 

 this assertion, it may be said that 



PORTION OF THE MEDULLARY SUBSTANCE OF THE 



in descending the animal series, 

 we see the glands becoming more 

 and more simplified, and trans- 

 formed 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 



LEAD; MAGNIFIED 300 DIAMETERS. 

 Medullary substance with capillary network, 

 fine reticulum of connective tissue , and a few 

 lymph corpuscles; 6, 6, Superficial lymph- 

 path, traversed by a reticulum of nucleated 

 cells (c c), with numerous anastomosing pro- 

 longations. The lymph corpuscles have for 

 the most part been removed ; d, c?, Trabeculae 

 composed almost exclusively of unstriped mus- 

 cular tissue ; g, A small medullary cord, or 

 bridge, containing a blood-vessel and numerous 

 lymph corpuscles. 



regions simple plexuses ; in rep- 

 tiles and fishes, the lymphatic glands 

 disappear altogether, and the plexuses that replace them are themselves not 

 at all complicated." Sappey. 



PREPARATION OF THE LYMPHATIC VESSELS. The lymphatic networks can only be 

 studied after having been filled with mercury by means of injection ; but as this opera- 

 tion is not usually practised by the pupils for whom this book is written, the mode of 

 performing it will only be traced in a few words. 



The apparatus in use consists of a glass tube continued by a flexible one, which 

 carries at its inferior extremity an iron tap and a fine canula, also of iron, or (better) glass. 

 To apply this apparatus, the tube ought to be suspended and then filled with mercury ; 

 the canula is then seized by the right hand, keeping it parallel to the membrane we 

 wish to inject, and burying it in the most superficial layer of that membrane. The 

 extremity of the canula is thus introduced into the midst of the meshes of the lymphatic 

 network, and necessarily wounds some of the capillaries which compose it. In opening 

 the tap, the mercury is allowed to flow into the capillaries by the solutions of continuity 

 they present, and fills them in the most perfect manner. The lymphatic plexuses being 



