958 THE DIGESTIVE SYSTEM. 
Il. Compound glands.—Duct divided. 
(7) Compound tubular-—Branched elongated tubes, no acini—e.g. testes, kidney, most 
gastric glands. 
(6) Compound acinous or alveolar (racemose glands), branched duct with saccular acini 
on terminal branches—e.g. salivary, sebaceous, and Meibomian glands ; the mucous 
glands of the mouth, tongue, palate, pharynx, nose, cesophagus, and respiratory tube. 
(c) Acino-tubular.—Branched duct, with elongated narrow acini on terminal branches—e.g. 
pancreas, Brunner’s glands, prostate. 
IIl. Solid gland.—The liver. 
To save confusion it may be pointed out that instead of acinus the term alveolus (and also 
saccule and follicle) is often used, and also that the term “racemose gland” is often conveniently 
used instead of compound acinous gland. - 
General Structure of Glands.—Whilst the small glands, such as those of the 
mouth and pharynx, are placed in the mucosa or submucosa immediately beneath the 
point at which their ducts open on the surface, the large glands form distinct masses, 
generally surrounded by special capsules, and often lie at a considerable distance from 
the points at which their ducts open. 
One of these large glands of the acinous type, such as the parotid or submaxillary, 
presents the following general arrangement. The gland is made up, as can be seen 
with the unaided eye, of a number of masses, often as large as peas, which are surrounded 
and held together by connective tissue. These are known as lobes, and to each a 
branch of the duct passes. The lobes are in turn made up of a number of smaller 
masses—lobules—each having a special branch of the lobar duct. These again are com- 
posed of smaller lobules, and so on to a varying degree. Finally, the smallest are made 
up of a terminal branch of the duct, with a cluster of acini or alveoli developed upon it. 
The acini or alveoli, the special secreting portions of the gland, are composed of a 
basement membrane, often fenestrated or basket-like, formed of flattened cells, on the 
outer side of which the blood and lymph vessels lie. ‘The inner surface of this membrane 
is lined by the secreting epithelial cells, usually polygonal in shape, which almost com- 
pletely fill the alveolus. A small lumen, however, is left, into which the secretion of the cells 
is shed, whence it passes 
into the duct of the 
lobule, and thus to the 
main duct. 
The blood-vessels and 
lymphatics, on entering 
the gland, break up and 
run, branching as they 
go, in the connective 
tissue which conveys 
them to all parts of the 
gland. | 
Mucous and Serous | 
Glands.—Two distinct | 
varieties of salivary | 
glands are found, the 
; serous and the mucous, 
so Crescent of Gianuzzi differing not only in the 
An alveolus with secreting cell nature of their secretion, 
Connective tissue but also in the character 
of the epithelium lining 
their alveoli. In those 
In the serous gland the granular secreting cells and the centrally-placed nucleus on) une mR Uys 
should be noted. The relatively clear cells, with the dark crescents of (F ig. 645) the epithe- 
Gianuzzi, are distinctive in the mucous gland. lial cells are large, clear, 
or faintly granular, and 
the nucleus lies as a rule near the base of the cell. In addition, many mucous glands, 
but not all, have small flattened or crescentic cells, distinctly granular, which stain 
strongly with ordinary stains, lying between the basement membrane and the bases of 
the chief cells. These are the crescents or demilunes of Gianuzz. 
In the acini or alveoli of serous glands, on the other hand (Fig. 645), the epithelial 
cells are distinctly granular, the granules staining well with ordinary stains ; the nuclei 
are rounded and lie near the centre of the cells, and no demilunes are present. 
In man the parotid and the small glands which open into the fossz of the circum- 
Small duct from an alveolus 
Large duct 
Duet 
Fic. 645.—-SECTION OF A SEROUS GLAND ON THE LEFT, A Mucous GLAND 
ON THE RIGHT SIDE (Bohm and vy. Davidoff). 
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