GLANDS. 957 
fibres. (3) The glossopharyngeal nerve passes forwards beneath the upper part of the hyoglossus, 
and sends its terminal branches to the mucous membrane of the posterior third of the tongue, 
supplying the cireumvallate papillie, and the part of the tongue behind these, with both gustatory 
and common sensory fibres. (4) The internal laryngeal nerve also distributes a few fibres to the 
posterior part of the base of the tongue, near the epiglottis. 
The lymphatics of the anterior half of the tongue pass down through the floor of the mouth 
and join the submaxillary lymphatic glands. Those from the posterior half run with the ranine 
vein across the hyoglossus muscle (where they are connected with some small lingual glands) and 
joi the deep cervical glands. 
GLANDS. 
Various organs, differing widely both in structure and function, are commonly 
included under the general term glands. It is made to embrace: (@) the glands 
with ducts, such as the digestive glands (liver, pancreas, salivary glands, ete.), the 
sweat and sebaceous glands of the skin, the testes, etc., and the small glands 
embedded in the walls of the digestive and respiratory tracts; (1) the so-called 
ductless glands (spleen, thyroid, suprarenals, etc.), which possess no duets, but 
throw their secretions into the blood or lymph passing through them; and (¢) the 
lymphatic glands, which cannot properly be classitied under either of the other 
groups. We shall here consider only the true glands—namely, those included in the 
first group mentioned above, which are all characterised by the possession of ducts ; 
and what follows refers to them alone. 
A gland may be defined as an epithelial organ which separates or elaborates from the blood 
some substance which is either to be discharged from the body or used further in the economy. 
The product of the activity of the gland is known as its secretion, and the secretion is conveyed 
to its destination in all true glands, as explained above, by the gland duct. 
Every gland is primarily an outgrowth of the epithelium from the surface to which the secre- 
tion of the gland is to be subsequently conveyed. This outgrowth may remain undivided, con- 
stituting a simple gland. On the other hand, it may break up into two or more branches, giving 
rise to a compound gland. We thus arrive at the two great classes of glands—simple and 
compound. 
A simple gland may remain tubular, when it is known as a sumple tubular gland, of which 
Lieberkuhw’s follicles in the wall of the small intestine and the sweat glands are examples. Or 
it may be dilated at its extremity, the enlargement being known as an acinus (akwos, a grape or 
grape-stone) or alveolus, thus constituting a simple aetnous or alveolar gland, of which there are 
few examples in man (viz. some sebaceous glands), though they are numerous in the skin of the 
frog, ete. This gives us two varieties of simple glands—tubular and acinous or alveolar. 
Similarly a compound gland may remain tubular, constituting a compound tubular gland, such 
as the kidney, testicle, and the majority of the gastric glands. Or, on the other hand, the 
terminal branches of its ducts may be beset with dilatations (¢.¢. acini or alveoli), giving rise to 
a compound acinous or alveolar gland, which latter, owing to a remote resemblance presented by 
its clustering lobules to a miniature bunch of grapes, is often known as a racemose gland (racemus, a 
cluster). Most of the glands of the body are examples of this variety—eg. the salivary glands, the 
small glands of the mouth, tongue, pharynx, cesophagus, respiratory passages, eyelids, etc. Thus 
we arrive at two varieties of compound glands also—tubular and acinous or alveolar. 
A compound acinous (racemose) gland is composed of a main duct which branches and 
re-branches more or less freely according to the size of the gland, and the terminal divisions of 
which end finally in specialised secreting parts, the acini or alveoli, quite distinguishable from 
the ducts or conducting parts. In true acinous glands the acini or alveoli are distinctly saccular ; 
in other glands, such as the pancreas, this is not the case, the acini being long and narrow. 
Accordingly, the term acino-tubular has been introduced and applied to glands of this latter 
type, which is usually made to include the pancreas, the prostate, and Brunner’s glands.! 
It should be added that the term acino-tubular is by some authors used exclusively instead 
of acinous for all racemose glands. 
There is one gland, however, which cannot be included in any of the above varieties, and 
which must be placed in a class by itself. This is the liver. It is composed of an enormous 
number of small secreting lobules, between which run the branches of the bile-duct. These 
lobules in the mammalian liver cannot in any way be compared to acini, or to collections of acini, 
as their cells are not arranged around a central lumen, but form a practically solid mass, with 
minute bile capillaries running everywhere between them. It might in mammals, for want of a 
better term, be classed as a solid gland. 
The foregoing may be summarised in tabular form thus :— 
I. Simple glands.—Duct undivided. 
(a) Simple tubular—Undilated at end—e.g. Lieberkiihn’s follicles, sweat, and many gastric 
glands. 
(b) Simple acinous (alveolar or saccular)— Dilated at end—e.g. some sebaceous glands (rare). 
1 Some authorities consider the glands of Brunner to belong to the class of compound tubular glands 
(Heidenhain, Watney, Jonnesco, etc.). 
i, 
