262 THE HUMAN BODY. 



secreting surface in various ways so that a large surface can- 

 be packed in a small bulk, just as a Chinese lantern when 

 shut up occupies much less space than when extended, 

 although its actual surface remains of the same extent. In 

 a few cases the folding takes the form of protrusions into- 

 the cavity of the secreting organ as indicated at C, Fig. 88, 

 and found on some synovia! membranes; but much more 

 commonly the surface extension is attained in another way, 

 the basement membrane, covered by its epithelium, being 

 pitted in or involuted as at B. Such a secreting organ i& 

 known as a gland. 



Forms of Glands. In some cases the surface involu- 

 tions are uniform in diameter, or nearly so, throughout (B, 

 Fig. 88). Such glands are known as tubular; examples 

 are found in the lining coat of the stomach (Fig. 97*);alsa 

 in the skin (Fig.l20f), where they form the sweat-glands. 

 In other cases the involution swells out at its deeper end and 

 becomes more or less sacculated (E] ; such glands are racemose 

 or acinous. The small glands which form the oily matter 

 poured out on the hairs (Fig. 119 1) are of this type. In both 

 kinds the lining cells near the deeper end are commonly 

 different in character from the rest; and around that part 

 of the gland the blood-vessels form a closer network. 

 These deeper cells form the true secreting elements of the 

 gland, and the passage, lined with different cells, leading 

 from them to the surface, and serving merely to carry off 

 the secretion, is known as the gland dud. When the duct 

 is undivided the gland is simple; but when, as is more 

 usual, it is branched and each branch has a true secreting 

 part at its end, we get a compound gland, tubular (G) or 

 racemose ( F, IT) as the case may be. In such cases the 

 main duct, into which the rest open, is often of considera- 

 ble length, so that the secretion is poured out at some dis- 

 tance from the main mass of the gland. 



A fully formed gland, H, thus comes to be a complex 

 structure, consisting primarily of a duct, c, ductules, dd, 

 and secreting recesses, ee. The ducts and ductules are 

 lined with epithelium which is merely protective and differs 

 in character from the secreting epithelium which lines the 



* P. 319. f P. 418. J P. 416. 



