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THE LYMPHATIC SYSTEM 



THE LYMPH NODULES. 



These are oval or round, densely packed masses of lymphocytes 

 supported in a reticulum of connective tissue. They vary in size 

 and are commonly located singly in the subepithelial connective 

 tissue along the extent of the digesti^'e and respiratory tract. Each 

 nodule has a connective-tissue framework within whose meshes are 

 lymphocytes in various stages of development. The central, more 

 diffuse region of a nodule, known as the germinal center, is occupied 

 by the less differentiated cells. This is a region of mitotic activity, 

 from which new cells become differentiated and are pushed toward 

 the periphery. 



Agminated Lymph Nodules.— There are groups of nodules located 

 along side one another in the subepithelial connective tissue of the 

 digestive tract. In the ileum of mammals, near its junction with the 

 large intestine, are groupings of many nodules, called Peyer's 

 patches. (Fig. 71.) Some of these extend through the epithelium 



Fig. 71. — A group of nodules (Peyer's patch) below the epitheUum of the ileum of 



the dog. 



into the lumen of the intestine and also into the submucosal coat. 

 Another collection of nodules ocurs in the connective tissue adjoin- 

 ing the epithelium of the cecum and vermiform appendix. 



Tonsils. — In mammals, several prominent aggregations of lymj^ih 

 nodules, known as tonsils, are found in the pharynx. They differ in 

 location but have a similar organization. A group composing the 

 faucial or palatine tonsils is located on each side of the ])haryngeal 

 cavity between the pillars of the fauces. The lingual tonsil is located 



