THYMUS GLAND. 



125 



septa of connective tissue, along which the blood-vessels and lymphatics 

 pass to and from the lobules. Each lobule shows plainly, when 

 examined with the low power, a distinction into an outer cortical and 

 an inner medullary portion. The cortical part of the lobule is imper- 

 fectly divided into nodules by trabeculse of connective tissue, and is 

 very similar in structure to the lymphoid tissue of the lymphatic 

 glands and tonsils, with which it also agrees in exhibiting numerous 

 indications of indirect cell-division, but the medulla is more open in its 

 texture, and the reticulum is composed of larger, more transparent, 

 flattened cells, and contains fewer lymph-corpuscles. Moreover, there 

 are found in the medulla peculiar concentrically striated bodies (the 

 concentric corpuscles, fig. 150), which are " nests " of flattened epithelial- 

 cells arranged concentrically around one or more central cells. Some- 

 times these corpuscles are compound, two or three being grouped 

 together and similarly inclosed by flattened cells. The lymphoid tissue 

 is abundantly supplied with capillary blood-vessels, and large lymphatic 

 vessels issue from the organ, but in what way the latter are connected 

 with the lobules has not been ascertained. 



FlG. 149. A LOBULE OF THE THYMUS OF A CHILD, AS SEEN UNDER A LOW POWER. 

 c, cortex ; c, concentric corpuscles within medulla ; b, blood-vessels ; tr, trabeculse. 



Lymphoid tissue occurs in many other parts of the body in addition 

 to the lymphatic glands, tonsils, and thymus gland, although it may 

 not, as in these structures, constitute the bulk of the organ. Thus it is 

 found in many mucous membranes, such as those of the intestine and 

 of the respiratory tract, both in a diffuse form and also collected into 



