146 



THE LYMPHATIC SYSTEM 



the age of the individual. In most portions it is no more than a 

 pavement epithelium, but over the surface of the functionally 

 active ovary these cells are much thickened and acquire a cuboidal 



shape ; thus it 

 forms the " germi- 

 nal epithelium " 

 of the ovary. In 

 young individuals, 

 viz., in fetal life 

 and early child- 

 hood, the cuboidal 

 cell type is found 

 in many portions 

 of the peritoneum, 

 pleura, and peri- 

 cardium. 



The synovial 

 membranes resem- 

 ble the serous in 

 their structure. 

 They are lined by 

 a single layer of 

 pavement cells 

 which is said to 

 be incomplete in places. Its endothelium is supported upon a 

 layer of firm fibrous tissue richly supplied with both lymphatic and 

 blood capillaries. In the recesses of the joints the synovial mem- 

 branes are frequently thrown into small villous folds, which are 

 chiefly formed by the inner portion of the fibrous coat and are 

 covered with endothelium ; these are the synovial villi. 



The bursae and the synovial sheaths of the tendons are of simi- 

 lar structure. 



Both the serous and the synovial membranes are moistened by 

 fluid which contains leucocytes in small numbers, and closely re- 

 sembles the lymph and tissue juice in its composition. 



LYMPHATIC FOLLICLES (Lymphatic Nodules). The lym- 

 phatic follicle is a structural unit of lymphoid tissue which may 

 exist independently, as in the solitary follicles of the intestinal 

 tract, or may form groups or accumulations consisting of a 

 greater or less number of f ollicular units. In this latter condition 

 they occur in the mucous membrane of the small intestine as 



FIG. 145. SECTION OF A VASCULAR SYNOVIAL VILLUS FROM 



THE KNEE JOINT OF A CHILD. 

 Hematein and eosin. Photo, x 200. 



