GLANDS 57 



Such glands as have been described, either branched or unbranched, 

 occur in great numbers as constituent parts of some organ, and they are 

 classed as simple glands. The sebaceous and sweat glands of the skin, 

 intestinal glands, and uterine glands are examples of this class. Many 

 glands are much larger than these, owing to the fact that the epithelial 

 outgrowth has branched repeatedly. It becomes invested with a con- 

 nective tissue capsule, which sends partitions, or septa, among the ramifi- 

 cations of the epithelial tube, thus dividing the gland into lobes and lob- 

 ules. A lobule usually contains a terminal branch of the duct together 

 with the cluster of end pieces which empty into it. The large glands not 

 only have a connective tissue framework, but also a special supply of 

 nerves, blood vessels and lymphatic vessels. Thus they form independent 

 organs, and they are classed as compound glands. They include the liver, 

 which discharges its secretion through a single duct; the pancreas, which 

 is formed by the fusion of two glands and therefore has primarily two 

 ducts; and many smaller organs, like the pros- 

 tate, which is a compact group of glands each 

 of which has a separate duct. 



All the glands thus far considered are alike 

 in being outpocketings of epithelium. Most of 

 them develop as masses or cords of epithelial 

 cells which later acquire a central cavity or 

 lumen. The secreting cells may discharge their 

 products from their free surfaces directly into 

 the lumen; or the secretion may enter minute 



canals, either within the cells (intracellular), or FlG< 48 ._Di7^A^F A SIMPLE AL- 

 between the cells (intercellular). Intercellular 

 secretory canals (also called capillaries) are 



found in the serous glands of the tongue and 



in the serous portions of the salivary glands; they occur also in the 

 liver, the gastric and pyloric glands, sweat glands, lachrymal gland and 

 bulbo-urethral gland. Various forms are shown in the right half of the 

 diagram Fig. 48. They occur where two or more cells come together 

 and consequently they are in relation with two or more terminal bars. 

 In longitudinal sections the bars may be seen to extend downward along 

 the canals. Through such intercellular canals the basal cells in a glandu- 

 lar epithelium may discharge their secretion into the central cavity, as 

 shown in Fig. 48. Intracellular secretory canals, shown in the left half 

 of Fig. 48, are less definite in outline, and are never in relation with termi- 

 nal bars. They may be transient vacuoles opening at the surface. Some- 

 times they anastomose and form a network of canals within the cell. They 

 have been observed, together with intercellular canals, in the sweat 



