STRUCTURE 49 



In the interstitial lymphatic glands the lymphoid 

 nodules are arranged peripherally beneath the capsule 

 and they are the first to receive the entering lymph. 

 But the subepithelial lymphatic glands are distin- 

 guished by the absence of afferent lymphatic vessels. 

 (According to Lenart, Henke and others, quoted by 

 Pybus, 1915, injections of carmine into the nasal or 

 oral submucosa eventually find their way into the 

 tonsils on both sides. But it is quite possible that 

 escape of the injection material on to the surface might 

 enter the tonsil that way (see Chapter XIII.). An- 

 atomically, anyhow, afferent lymphatic vessels have 

 never been demonstated.) Here the lymphatic nodules 

 lie against the epithelium of the alimentary canal super- 

 ficial even to the muscularis mucosae. So close to the 

 epithelium do they lie that the lymphoid and the epi- 

 thelial cells are commonly mingled. There is a con- 

 tinuous passage of small glandular lymphocytes from 

 the lymphoid nodule through the epithelium into the 

 lumen of the alimentary canal and back again (see 

 further). 



The solitary lymph gland consists of a single such 

 nodule only. The nodule is drained by an efferent basal 

 lymphatic vessel which leads eventually to a mesen- 

 teric or other interstitial lymphatic gland. 



A Peyer's patch represents an aggregation of from 

 ten to sixty (Sobotta) lymphoid nodules. Each nodule 

 has one aspect close to the epithelial surface which is 

 here uncovered by villi. The human vermiform appen- 

 dix, according to the late Mr. Lockwood's estimate, 

 may be lined by as many as 150 to 200 lymphoid 

 nodules. 



In the case of the nasopharyngeal and faucial tonsils 

 the epithelial surface is much folded, thus permitting 

 a great collection of lymph nodules in a small space 

 yet with each nodule abutting the surface epithelium. 



