88 



GENERAL ANATOMY. 



structure of the liver is so complex that it can hardly yet be regarded as known 

 with absolute certainty, while there are a great many glands which consist 



either of a single tube lined with epithelium, on 

 the outer side of which the blood circulates, or 



[Fig. 48. 



Three plans, a, b, c, of supposed sec- 

 tions of secreting membranes, to show 

 general arrangement of their compo- 

 nent structures, and the way in which 

 their surfaces are increased. In all 

 three plans, the broad shaded line re- 

 presents the areolo-vascular layer, the 

 thin solid line is the basement or limit- 

 ing membrane, and the dotted line the 

 epithelial or covering layer, a, shows 

 an increase by simple plaited or fringed 

 projections; b, five modes of increase 

 by recesses, forming five kinds of sim- 

 ple glands, viz., 1, a tubular follicle or 

 crypt; 2, a saccular follicle or sac; 3, 

 a coiled tube ; 4, a multilocular tube, 

 that is, a tube with depressions in it; 

 5, a multilocular sac. c, shows two 

 forms of compound glands ; 6, branch- 

 ed tubes forming a compound tubular 

 gland ; 7, branched tubes ending in 

 little recesses or vesicles, forming a 

 compound racemose or conglomerate 

 gland. (After Sharpey.)] 



even a simple closed sac which opens when it 

 becomes charged with secretion. 



The great majority of glands, however, can be 

 reduced ideally to a very simple form, viz., to an 

 involution more or less complex of the basement- 

 membrane, carrying of course its epithelium with 

 it, and having the capillary vessels distributed on 

 its attached surface (Fig. 48). If this involution 

 be perfectly simple, an open tube results, as in the 

 stomach (see Fig. 400), or the common mucous 

 crypts of the urethra (Figs. 404, 406); and should 

 the mouth of such a tube become closed, a simple 

 follicle is formed, as in the intestine. Branches 

 projecting out from the bottom of this tube con- 

 stitute the simplest form of racemose gland. The 

 most rudimentary condition of such a gland is 

 shown in the branched tubes of the gastric mu- 

 cous membrane in Figure 400. If such a tube be 

 conceived of as divided into branches as well as 

 branching out at its extremity, we have a com- 

 pound racemose gland consisting of a single 

 lobule terminating in its duct (such as Brunner's 

 glands), and an aggregation of such lobules may 

 all open into a common duct, or may have a great 

 number of separate ducts. Instances of such 

 glands will be found in the salivary glands, the 

 pancreas, &c. Or the necessary extent of epithe- 

 lial surface may be obtained by the duct being 

 coiled on itself, as in the sweat-glands (Fig. 41, 

 page 79), or the extremity of the duct only may 

 be thus arranged (Fig. 370). In other glands, 

 as in the kidney, the mucous duct is undivided 

 from the beginning, and the capillaries from 

 which the secretion is to be eliminated are dis- 

 tributed upon its walls or project into its ampul- 

 lated commencement (Fig. 335). 



For the description of the Ductless or Blood 

 Glands, we must refer to the sections in the text 

 relating to the Anatomy of the Spleen, Suprarenal Capsules, Thyroid, and 

 Thymus. 



