170 MICROSCOPIC ANATOMY OF THE ORGANS. 



tonsils into the mouth cavity through the epithelium begins 

 early. It may be noticed in the eighth month of foetal life, 

 and increases after this. 



The palatine tonsils arise, according to His, in a depression 

 which represents the space between the second and third bran- 

 chial arches. This is clothed by the mucous membrane of the 

 mouth cavity. The crypts are formed by the downward growth 

 of solid masses of cells from the epithelium (Stohr), a process 

 which occurs at the end of the fourth month in the life of the 

 human foetus, and continues throughout the entire fcetal life and 

 for the first year or two after birth. The solid masses of cells 

 later on become hollow and give rise to the blind canals or 

 crypts of the adult organ. In the connective tissue of the 

 mucous membrane leucocytes begin to gather from the blood- 

 vessels during the third month. This continues up to the time 

 of birth, and it is only during the first year after birth that 

 definite follicles with germinal centres are to be found. 



5. Glands of the Mouth Cavity. 



Under this heading are to be discussed the large salivary 

 glands whose ducts open into the mouth cavity i. e., the 

 parotid, submaxillary, and sublingual glands, as well as the 

 smaller glands which are named according to their situation. 

 All the glands of the mouth may be divided, according to their 

 products, into: 1, Serous glands, which secrete an albuminous 

 serous fluid ; 2, Mucous glands, which produce a mucin-con- 

 taining secretion ; and 3, Mixed glands, which simultaneously 

 secrete both kinds of fluid. 



All these glands are tubular. The smaller are simple 

 branched tubular, while the larger are compound tubular 

 glands. The latter are capable of division into larger and 

 smaller lobules, which are separated by connective tissue (Fig. 

 126). Each lobule contains ducts which divide in its interior. 

 The small lobules correspond with simple branched tubular 

 glands. 



The ducts in the lobules are more or less curved, so that 



