MODIFICATIONS IN FORM OF THE SECRETING SURFACE. 



399 



is often enlarged, is spoken of as the " fundus " of the gland. If compound, its 

 terminations are known as "alveoli." In a simple gland the shape of the cavity 

 may be tubular (fig. 457, g} or saccular (h) : of these two kinds of simple gland the 

 former is by far the more common. Examples of simple saccular glands are found 

 in the skin of the frog (fig. 458) of simple tubular glands in the intestines (fig. 459). 

 The secreting surface may be increased, in a simple tubular gland, by mere lengthening 

 of the tube, in which case, however, when it acquires considerable length, the tube is 

 coiled up into a ball (fig. 457, '), so as to take up less room, and adapt itself to receive 

 compactly ramified blood-vessels. The sweat-glands of the skin are instances of simple 

 glands formed of a long convoluted tube. But the chief means observed of further 



Fig. 457. PLANS OF EXTENSION OF SECRETING MEMBRANE, BY INVERSION OR RECESSION. (Sharpey.) 



A, simple glands, viz., g, straight tube ; h, sac ; i, coiled tube. B, simple glands with loculated 

 walls ; k, of tubular form ; I, saccular. C, racemose, or acinous compound gland ; m, entire gland, 

 showing branched duct and tabular structure ; n, a lobule, detached with o, branch of duct proceeding 

 from it. D, compound tubular gland. 



B and C represent rather the embryonic than the permanent condition of the acinous glands ; 

 the actual condition of the alveoli in the adult condition being more like those shown in fig. 460. 



increasing the secreting surface is by the subdivision, as well as extension, of the 

 cavity, and when this occurs the gland is said to be compound. There is, however, a 

 condition sometimes met with, in which the sides or extremity of a simple tube or 

 sac merely become pouched or loculated (fig. 457, Jc, 7), in which case the tube 

 is termed the gland duct, cr, as in Brunner's glands, and the small mucous glands 

 generally, the pouchings or loculations may grow out into irregular tubular alveoli ; 

 the gland is however still to be regarded as simple, since all the alveoli open into a 

 single duct (Flemming). 



In the compound glands, the divisions of the secreting cavity may assume a 

 tubular or a saccular form, and this leads to the distinction of these glands into the 

 " tubular," and the "acinous," or " racemose." The latter were so termed from the 

 superficial resemblance which they bear, when examined with a lens, to a bunch of 

 grapes. But it is found in most cases when their subdivisions are unravelled, 

 that the apparent saccules are merely dilatations in the course of somewhat irregu- 

 larly branching tubules (fig. 462); the glands are hence often named "acino-tubular.' 



The disuse of the term racemose or acinous, as applied to these glands, has been advocated 

 by Flemming on the ground that, as is well known, in many of these glands the terminal 

 alveoli are not merely dilatations grouped around the endings of the ducts, but are distinctly 



