GLANDS. 99 



are formed by a duct, which, when traced from its 

 orifice, is found, most generally, to remain undivided, 

 and to terminate in a solitary bulb, or coecal pouch, 

 of considerable size (PL XVIII. fig. II.). The inter- structure. 

 nal surface of this pouch is covered with depressions, 

 which represent the vesicles of the glands we have 

 already described. Sometimes a group of these de- 

 pressions, becoming deeper, isolate themselves incom- 

 pletely from the common cavity, by a partially 

 formed neck, or pedicle, and thus constitute a lobule 

 (fig. III. 2). The wall proper of the sac, or pouch, 

 is structureless, and very thin, but it is strengthened 

 by an external layer of fibrillated tissue (PL XVIII. 

 fig. II. 5). In contact with its inner surface are one 

 or two layers of young cells, with finely granular and 

 transparent contents, and nuclei which are quite dis- 

 tinct (fig. II. 2). Upon this epithelial layer are 

 numerous other cells, differing from those just de- 

 scribed, both in volume, and in their contents. They 

 increase in size, in fact, exactly in proportion as we 

 trace them nearer to the centre of the gland cavity ; 

 and during their growth in size, the nucleus disap- 

 pears, and their contents are transformed into oil- 

 globules (fig. II. 1 ; fig, IV. ; fig. V. 2). Finally, near 

 the orifice of the duct, these cells, having attained the 

 maximum of their development, and being no longer 

 able to resist the pressure from all sides of the cavity, 

 the contents of which are thus constantly increasing, 

 rupture their cell walls, and give forth a sort of greasy 

 substance which, in short, is the true secretion of the 

 sebaceous gland (PL XVIII. fig. II. 4). The excre- 

 tory canal generally opens into a hair follicle; but 



