334 HANDBOOK OF PHYSIOLOGY. 



mose glands. They are made up of lobules. Each lobule consists of the 

 branchings of a subdivision of the main duct of the gland, which is gen- 

 erally more or less convoluted toward its extremities, and sometimes, ac- 

 cording to some observers, sacculated or pouched. The convoluted or 

 pouched portions form the alveoli, or proper secreting parts of the gland. 

 The alveoli are composed of a basement membrane of flattened cells 

 joined together by processes to produce a fenestrated membrane, the 

 spaces of which are occupied by a homogeneous ground-substance. With- 

 in, upon this membrane, which forms the tube, the nucleated salivary 

 secreting cells, of cubical or columnar form, are arranged parallel to one 

 another enclosing a central canal. The granular appearance frequently 

 seen in the salivary cells is due to the numerous zymogen granules which 

 they contain. When isolated, the cells not infrequently are found to be 

 branched. Connecting the alveoli into lobules is a considerable amount 



Fig. 234. -Section of sub-maxillary gland of dog. Showing gland cells, 6, and a duct, a, in section. 



(Kolliker.) 



of fibrous connective tissue, which contains both flattened and granular 

 protoplasmic cells, lymph corpuscles, and in some cases fat cells. The 

 lobules are connected to form larger lobules (lobes), in a similar manner. 

 The alveoli pass into the intralobular ducts by a narrowed portion (inter- 

 calary), lined with flattened epithelium with elongated nuclei. The in- 

 tercalary duets pass into the intralobular ducts by a narrowed neck, lined 

 with cubical cells with small nuclei. The intralobular duct is larger in 

 size, and is lined with large columnar nucleated cells, the parts of which, 

 toward the lumen of the tube, present a fine longtitudinal striation, due 

 to the arrangement of the cell network. It is most marked in the sub- 

 maxillary gland. The intralobular ducts pass into the larger ducts, and 

 these into the main duct of the gland. As these ducts become larger 

 they acquire an outside coating of connective tissue, and later on some 

 unstriped muscular fibres. The lining of the larger ducts consist of one 

 or more layers of columnar epithelium, the cells of which contain an 

 intracellular network of fibres arranged longitudinally. 



