668 PHYSIOLOGY OF DIGESTION AND SECRETION. 



pass close to this ganglion, but Langley has shown that only those 

 destined for the sublingual gland really connect with the nerve 

 cells of the ganglion, and he suggests, therefore, that it should 

 be called the sublingual instead of the submaxillary ganglion. The 

 nerve fibers for the submaxillary gland make connections with nerve 

 cells lying mainly within the hilus of the gland itself. The supply 

 of sympathetic autonomics has the same general course as those 

 for the parotid, namely, through the cervical sympathetic to the 

 superior cervical ganglion and thence to the glands. 



Histological Structure. The salivary glands belong to the type 

 of compound tubular glands. That is, the secreting portions are 

 tubular in shape, although in cross-sections these tubes may pre- 

 sent various outlines according as the plane of the section passes 

 through them. The parotid is described usually as a typical serous 

 or albuminous gland. Its secreting epithelium is composed of cells 

 which in the fresh condition as well as in preserved specimens contain 

 numerous fine granules and its secretion contains some albumin. 

 The submaxillary gland differs in histology in different animals. 

 In some, as the dog or cat, the secretory tubes are composed chiefly 

 or exclusively of epithelial cells of the mucous type. In man the 

 gland is of a mixed type, the secretory tubes containing both mucous 

 and albuminous cells. The sublingual gland in man also contains 

 both varieties of cells, although the mucous cells predominate. In 

 accordance with these histological characteristics it is found that the 

 secretion from the submaxillary and sublingual glands is thick and 

 mucilaginous as compared with that from the parotid. 



In the mucous glands another variety of cell, the so-called demilunes or 

 crescent cells, is frequently met with, and the physiological significance of 

 these cells has been the subject of much discussion. The demilunes are 

 crescent-shaped, granular cells lying between the mucous cells and the base- 

 ment membrane, and not in contact, therefore, with the central lumen of 

 the tube. According to Heidenhain, these demilunes are for the purpose 

 of replacing the mucous cells. In consequence of long-continued activity 

 the mucous cells may disintegrate and disappear, and the demilunes then 

 develop into new mucous cells. Another view is that the demilunes represent 

 distinct secretory cells of the albuminous type, while others assert that they 

 are a specific type of cell with probably specific functions.* 



The salivary glands possess definite secretory nerves which when 

 stimulated cause the formation of a secretion. This fact indicates 

 that there must be a direct contact of some kind between the gland 

 cells and the terminations of the secretory fibers. The ending of the 

 nerve fibers in the submaxillary and sublingual glands has been de- 

 scribed by a number of observers.! The accounts differ somewhat as 

 to details of the finer anatomy, but it seems to be clearly established 

 that the secretory fibers from the chorda tympani end first around the 



* See Noll, " Archiv f . Physiologie, " 1902, suppl. volume, 166. 

 f See Huber, " Journal of Experimental Medicine," 1, 281, 1896. 



