280 THE SALIVARY GLANDS. 



sub-mucosa, whilst the finer twigs penetrate into the papillae, where they form 

 either a capillary net- work or simple loops. 



The larger lymphatics lie in the sub-mucosa, whilst the finer branches 

 form a fine net-work placed in the mucosa. The lymph-follicles also belong 

 to the lymphatic system. On the dorsum of the posterior part of the tongue they 

 form an almost continuous layer. They are round or oval (1-1*5 mm. in diameter), 

 and placed in the sub-mucosa. They consist of adenoid tissue loaded with lymph - 

 corpuscles. The outer part of the adenoid reticulum is compressed so as to form 

 a kind of capsule for each follicle. Similar follicles occur in the intestine as 

 solitary follicles, in the small intestine they are collected together into Peyer's 

 patches, and in the spleen they occur as Malpighian corpuscles. On the dorsum 

 of the tongue several of these follicles form a slightly oval elevation, which is 

 surrounded by connective tissue. In the centre of this elevation there is a depres- 

 sion into which a mucous gland opens, which fills the small crater with mucus. 



The Tonsils have fundamentally the same structure. On their surface are 

 a number of depressions into which the ducts of small mucous glands open. These 

 depressions are surrounded by groups (10-20) of lymph-follicles, and the whole 

 is environed by a capsule of connective tissue. After E. H. Weber discovered 

 lymphatics in the neighbourhood of the tonsils, Briicke referred these structures to 

 the lymphatic system. Large lymph-spaces, communicating with lymphatics, occur 

 in the neighbourhood of the tonsils, but as yet a direct connection between the 

 spaces in the follicles and the lymph-vessels has not been proved to exist. 

 Stohr found that numerous leucocytes passed between the epithelium covering 

 the tonsils, and reached the mouth. 



Nerves- Numerous medullated nerve-fibres occur in the sub-mucosa, pass into 

 the mucosa and terminate partly in the individual papillae in Krause's End-bulbs, 

 which are most abundant in the lips and soft palate, and not so numerous in the 

 cheeks and in the floor of the mouth. The nerves administer not only to common 

 sensation, but they also are the organs of transmission for tactile (heat and pres- 

 sure) impressions. It is highly probable, however, that some nerve-fibres end in 

 fine terminal fibrils, between the epithelial cells, such as occur in the cornea and 

 elsewhere. 



142. The Salivary Glands. 



Structure of the Ducts. The three pairs of salivary glands, sub- 

 maxillary, sub-lingual, and parotid, are compound tubular glands. 

 Fig. 116, A, shows a fine duct, terminating in the more or less flask- 

 shaped alveoli or acini. [Each gland consists of a number of lobes, 

 and each lobe in turn of a number of lobules, which, again, are 

 composed of acini. All these are held together by a framework of con- 

 nective tissue. The larger branches of the duct lie between the lobules, 

 and constitute the interlobular ducts, giving branches to each lobule which 

 they enter, constituting the intralobular ducts. These intralobular ducts 

 branch and finally terminate in connection with the alveoli, by means 

 of an intermediary or intercalary part. The larger interlobar and inter- 

 lobular ducts consist of a membrana propria, strengthened outside 

 with fibrous and elastic tissue, and in some places also by non-striped 

 muscle, while the ducts are lined by columnar epithelial cells. In the 

 largest branches, there is a second row of smaller cells, lying between 



