THE ORGANS OF DIGESTION. 



The sublingual gland is the smallest of the salivary glands. It is situated 

 beneath the mucous membrane of the floor of the mouth, at the side of the fraenum 

 linguae, in contact with the inner surface of the lower jaw, close to the symphysis. 

 It is narrow, flattened, in shape somewhat like an almond, and weighs about a 

 drachm. It is in relation, above, with the mucous membrane ; below, with the 

 Mylo-hyoid muscle; in front, with the depression on the side of the symphysis of 

 the lower jaw, and with its fellow of the opposite side ; behind, with the deep 

 part of the submaxillary gland ; and internally, with the Genio-hyo-glossus, 

 from which it is separated by the lingual nerve and Wharton's duct. Its 

 excretory ducts (ducts of Rivinus), from eight to twenty in number, open 

 separately into the mouth, on the elevated crest of mucous membrane caused by 

 the projection of the gland, on either side of the fraenum linguae. One or more 

 join to form a tube which opens into the Whartonian duct ; this is called the duct 

 of Bartholin. 



Vessels and Nerves. The sublingual gland is supplied with blood from the 

 sublingual and submental arteries. Its nerves are derived from the lingual. 



Structure of Salivary Glands. The salivary are compound racemose glands, 

 consisting of numerous lobes, which are made up of smaller lobules connected 

 together by dense areolar tissue, vessels, and ducts. Each lobule consists of the 

 ramifications of a single duct, " branching frequently in a tree-like manner," the 

 branches terminating in dilated ends or alveoli, on which the capillaries are 

 distributed. These alveoli, however, as Pfliiger points out, are not necessarily 

 spherical, though sometimes they assume that form ; sometimes they are perfectly 

 cylindrical, and very often they are mutually compressed. The alveoli are enclosed 

 by a basement membrane which is continuous with the membrana propria of the 

 duct. It presents a peculiar reticulated structure, having the appearance of a 

 basket with open meshes, and consisting of a network of branched and flattened 

 nucleated cells. 



The alveoli of the salivary glands are of two kinds, which differ both in the 

 appearance of their secreting cells, in their size, and in the nature of their 

 secretion. The one variety secretes a ropy fluid which contains mucin, and 

 has therefore been named the mucous, whilst the other secretes a thinner and 

 more watery fluid, which contains serum-albumin, and has been named serous 

 or albuminous. The sublingual gland may be regarded as an example of the 

 former variety, the parotid of the latter. The submaxillary is of the mixed 

 variety, containing both mucous and serous alveoli, the latter, however, prepon- 

 derating. 



Both alveoli are lined bv cells, and it is by the character of these cells that the 

 nature of the gland is chiefly to be determined, In addition, however, the alveoli 

 of the serous glands are smaller than those of the mucous ones. 



The cells in the mucous alveoli are spheroidal in shape, glassy, transparent, and 

 dimly striated in appearance. The nucleus is usuallv situated in the part of the 

 cell which is next the basement membrane, against which it is sometimes flattened. 

 The most remarkable peculiarity presented by these cells is, that they give off an 

 extremely fine process, which is curved in a direction parallel to the surface of the 

 alveolus, lies in contact with the membrana propria, and overlaps the process of 

 neighboring cells. The cells contain a quantity of mucin, to which their clear, 

 transparent appearance is due. 



Here and there in the alveoli are seen peculiar half-moon-shaped bodies lying 

 between the cells and the membrana propria of the alveolus. They are termed 

 the crescents of Crianuzzi or the demilunes of Heidenhain (Fig. 570), and are 

 regarded by Pfliiger as due to post-mortem change, but by most other later 

 observers they are believed to be composed of polyhedral granular cells, which 

 Heidenhain regards as young epithelial cells destined to supply the place of those 

 salivary cells which have undergone disintegration. This view, however, is not 

 accepted by Klein. 



Serous Alveoli. In the serous alveoli the cells almost completely fill the cavity. 



