THE DIGESTIVE TRACT. 



609 



ham and Lavdowsky, there are glandular formations of the race- 

 mose variety, such as those found in the nasal mucosa, which 

 are called serous glands, and which produce a watery secre- 

 tion. The parotid gland and the pancreas may also be grouped 

 with this variety. Others the sublingual gland discharge a 

 mucous, viscid liquid, while the secretion of the submaxillary 

 is partly serous and partly mucous. The differences in the 

 appearance of the glandular epithelia may be understood when 

 we recall the process of mucous secretion in general. (See page 

 329.) Epithelia not participating in the process of secretion are 



FIG. 261. NERVE-PLEXUS OF THE SMALL INTESTINE OF A CAT. 



MP, Meissner's plexus; S, subiuucous fibrous connective tissue; T, circular muscle of 

 the intestine, in transverse section ; AP, Auerbach's plexus ; L, longitudinal muscle of the 

 intestine, in longitudinal section. Magnified 800 diameters. 



found, according to E. Heidenhain, immediately beneath the 

 structureless layer, and are termed by him the bordering cells, 

 being the reserve from which epithelia are supplied to take the 

 place of those which were destroyed by the secretion of mucus. 

 .Such reserved epithelia are not found in serous glands for in- 

 stance, in the parotid. Different portions of the submaxillary 

 gland exhibit both varieties of the epithelia, which blend with 

 39 



