102 



THE ESSENTIALS OF HISTOLOGY 



The proper glandular substance (I. h.) is composed of lymphoid 

 tissue, i.e. a fine reticulum with the meshes thickly occupied by lymph- 

 corpuscles. It occupies all the interstices of the gland, forming com- 

 paratively large rounded masses in the cortex (lymphoid nodules, G) 

 between the' "trabecuhe, and smaller reticulating cord-like masses 

 (lymphoid cords, M) in the medulla. 



The cells which bridge across the lymph-channel in the medulla 

 (fig. 125, c) are branching nucleated cells which often contain pigment, 

 so that this part of the gland has a dark colour. The lymph-channel 

 is bridged across not only by these, but also by fibres derived from the 

 capsule and trabeculre, which pass to the lymphoid tissue and become 

 lost in its reticulum. But these fibres are often covered and concealed 

 by the branched cells. 



Lymphatic vessels (fig. 124, a. I.) enter the lymph-channels after 

 passing through the capsule, and the lymph is conveyed slowly along 

 the channels of the cortical and medullary part towards the hilus, 

 taking up many lymph-corpuscles in its passage. At the hilus it is 

 gathered up by an efferent vessel or vessels (e. I.) which take origin in 

 the lymph-sinuses of the medulla. 



An artery passes into each gland at the hilus ; its branches are 

 conveyed at first along the fibrous cords, but soon pass into the 

 lymphoid tissue, where they break up into capillaries (fig. 125, d)'. 

 The blood is returned by small veins, which are conducted along the 

 fibrous trabeculse to the hilus again. 



FlO. 126. A LOBULK OF THK THYMUS OV A CHIM> AS SEKN UNDER A LOW POWKR. 

 c, cortex ; M, medulla ; c, concentric corpuscles ; 6, blood-vessels ; Ir, trabeculae. 



The thymus gland is a lymphoid organ which is found only in the 

 embryo and during infancy. It is composed of a number of larger and 

 smaller lobules (fig. 126), which are separated from one another by 



