SECRETION. 219 



two sources. The cerebral fibres arise from the brain in the facial nerve and 

 pass out in the chorda tympani branch (Fig. 52). This latter nerve, after 

 emerging from the tympanic cavity through the Glaserian fissure, joins the 

 lingual nerve. After running; with this nerve for a short distance, the secre- 

 tory (and vaso-dilator) nerve-fibres destined for the submaxillary and sublin- 

 gual glands branch off and pass to the glands, following the course of the 

 ducts. Where the chorda tympani fibres leave the lingual there is a small 

 ganglion which has received the name of submaxillary ganglion. The nerve- 

 fibres to the glands 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-fibres for the 

 submaxillary gland make connections with nerve-cells mainly within the 

 hilus of the gland itself. The submaxillary and sublingual glands receive 

 also sympathetic nerve-fibres, which after leaving the superior cervical gan- 

 glion pass to the glands in the coats of the blood-vessels. 



Histological Structure. — The salivary glands belong to the type of com- 

 pound tubular glands, as Flemming has pointed out. That is, the secreting 

 portions are tubular in shape, although in cross sections these tubes may 

 present 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 con- 

 dition as well as in preserved specimens contain numerous fine granules (see 

 Figs. 53 and 55, A). Heidenhain states that in exceptional cases (in the 

 dog) some of the secreting cells may belong to the mucous type. The base- 

 ment membrane is composed of flattened branched connective-tissue cells, the 

 interstices between which are filled by a thin membrane. The submaxillary 

 gland differs in histology in different animals. In some, as the dog or cat, 

 all the secretory tubes are composed chiefly or exclusively of epithelial cells 

 of the mucous type (Fig. 56). 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. It follows from these histological characteristics that the secre- 

 tion from the submaxillary and sublingual glands is thick and mucilaginous as 

 compared with that from the parotid. 



In the mucous glands another variety of cells, 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 cres- 

 cent-shaped granular cells lying between the mucous cells and the basement 

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

 (see Fig. 56). 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. The most probable view at present is that the demi- 

 lunes represent distinct secretory cells of the albuminous type. 



