232 HANDBOOK OF PHYSIOLOGY. 



(intercalary), lined with flattened epithelium, with elongated nuclei. 

 The intercalary ducts 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, towards the lumen of the tube, present a fine longitudi- 

 nal striation, due to the arrangement of the cell network. It is most 

 marked in the submaxillary 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. 

 Varieties. Certain differences in the structure of salivary glands 



FIG. 175. FIG. 176. 



FIG. 175. From a section through a true salivary gland, a, the gland alveoli, lined with albu- 

 minous " salivary cells; 11 6, intralobular duct cut transversely. (Klein and Nob e Smith.) 



FIG. 176. From a section through a mucous gland in a quiescent state. The alveoli are lined 

 with transparent mucous cells, and outside these are the semilunes of Heidenhain. The cells should 

 have been represented as more or less granular. (Heidenhain.) 



may be observed according as the glands secrete pure saliva, or saliva 

 mixed with mucus, or pure mucus, and therefore the glands have been 

 classified as : 



(1) True salivary glands (called most unfortunately by some serous 

 glands), e. g., the parotid of man and other animals, and the submaxil- 

 lary of the rabbit and the guinea-pig (Fig. 175). In this kind the alve- 

 olar lumen is small, and the cells lining the tubule are short granular 

 columnar cells, with nuclei presenting the intranuclear network. Dur- 

 ing rest the cells become larger, highly granular, with obscured nuclei, 

 and the lumen becomes smaller. During activity, and after stimulation 

 of the sympathetic, the cells become smaller and their contents more 

 opaque ; the granules first of all disappearing from the outer part of the 

 cells, and then being found only at the extreme inner part and contigu- 

 ous border of the cell. The nuclei reappear, as does also the lumen. 



(2) In the true mucous-secreting glands, as the sublingual of man and 



