MOUTH CAVITY. 175 



work, which is separated from the gland cells by a thin mem- 

 brana propria. 



Non-medullated nerve fibres form a network at the mem- 

 brana propria, which is pierced by the small branches. They 

 become thickened in a varicose manner around the surfaces 

 of the gland cells. 



Having described briefly the general characteristics of the 

 glands of the mouth cavity, a few words will be of aid con- 

 cerning the peculiarities of each of these glands. 



The parotid is a purely serous gland in man and in most 

 animals (Figs. 126 and 127). The secretory capillaries are 

 seen very plainly between the gland cells. 



The submaxillary is in man and in the majority of animals 

 a mixed gland. In the rabbit it is purely serous. In man it 

 contains more serous than mucous tubules (Fig. 130). The 

 main duct has in the connective tissue a number of longitud- 

 inally disposed smooth muscle fibres. The framework of the 

 submaxillary gland consists of a well-marked capsule with 

 strands of connective tissue extending from it into the gland, 

 dividing it into lobules. Each acinus is surrounded by a deli- 

 cate basement membrane which has a distinctly fibrillar struct- 

 ure (Flint). These basement membranes are continuous with 

 a delicate fibrillar membrane enclosing each lobule. Elastic 

 fibres have been found surrounding the acini of the mucous 

 type. These are absent in serous alveoli. 



The ducts of the submaxillary have been studied by Flint 

 by means of the corrosive methods. In general the ducts 

 divide like the branches of a tree. The intralobular ducts lie 

 in the centre of the lobule. These pass on into the intercalary 

 ducts, into which the acini empty. The lumen of the acinus 

 has a dilated appearance, like an ampulla, at the end of the 

 intercalary duct (Fig. 132). From three to six ampullae empty 

 into each intercalary duct. 



Development of the Submaxillary. The gland appears at a 

 fairly early date as a mass of large epithelial cells arranged 

 partly in columns which represent the developing ducts and 

 alveoli. At the ends of these columns there are knob-like 



