234 



SECRETING GLANDS. 



brain, and the ciliary processes in the eye-ball, although secretion may 

 not be the primary office of the last-mentioned structures. In most of 

 these cases, the membrane assumes the form of projecting folds, which, 

 for the sake of further increase of surface, may be again plaited and 

 complicated, or cleft and fringed, at their borders (fig. 161, e,/). 



The plan of augmenting the secreting surface by recession or inver- 

 sion of the membrane, in form of a cavity, is, with few exceptions, that 



Fig. 161. 



Fig. 161. — Plan to Show Augmentation of Surface by Formation op 

 Processes. 



a, b, c, as in preceding figure ; d, simple, and ef, branclied or suljdivided processes. 



generally adopted in the construction of secreting glands. The first 

 degree is represented by a simple recess (fig, 1G2, //, //), and such a 

 recess, formed of secreting meml3rane, constitutes a simple gland. The 

 shape of the cavity may be tubular (//) or saccular (A), and, in either 

 case, it is called indifferently a crypt, follicle, or lacuna, for these names 

 have not been strictly distinguished in their application. Examples of 

 these simple glands are found in the mucous membrane of the stomach, 

 intestines, and uterus. 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. 102, ■/), so as to take up less room, and adapt itself to 

 receive compactly ramified blood-vessels. The sweat-glands, already 

 described, and the ceruininous glands of the ear are instances of simple 

 glands formed of a long convoluted tube. But the great means adopted 

 for further increasing the secreting surface is by the subdivision, as 

 well as extension, of the cavitj-, and when this occurs the gland is said 

 to be compound. There is, however, a condition which might be looked 

 on as a step between the simple and compound glands, in which the 

 sides or extremity of a simple tube or sac become pouched or loculated 

 /fig. 1C2, /", I). Tliis form might be named the multilocular crypt. 



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 " saccular," or " racemose." 



The racemose compound glands (fig. 1G2, c) contain a multitude of 

 saccules, opening in clusters, into the extremities of a branched tube, 

 named the excretory duct. The saccules are rounded, pyriform or 

 thimble-shaped, and then often named " ca3cal." They are as usual 

 formed by a proper or basement-membrane, and lined, or often rather 

 filled with secreting cells ; they are arranged in groups, round the 

 commencing branches of the duct, into which they open both terminally 

 and laterally (fig. 1G2, c, n); or it might with equal truth be said that 

 the branches of the duct are distended into clusters of saccular dilata- 

 tions. The ultimate branches of the duct open into larger branches (o), 



