THE CUTANEOUS GLANDS. 



333 



glands within the eyelid and the mammary glands. In all, the epithelial 

 tissues the secreting elements and the lining of the ducts are derivatives of 

 the ectoderm and, therefore, genetically related to the epidermis. 



The Sebaceous Glands. Although these structures, the glandula 

 sebace<z, are chiefly associated with the hair-follicles, they also occur, although 



Mouth 

 of gland 



Duct 



Alveoli 



Corium 



FIG. 379. Sebaceous glands in skin covering ala of nose. X 60. 



less frequently, independently and in those parts of the skin in which the 



hairs are wanting, as on the lips, prepuce, and labia minora. The size of 



these glands bears no relation to that of the hairs, since among the smallest 



(.2-. 4 mm.) are those on the scalp. The largest 



(.5-2; mm.) are found on the mons pubis, scrotum, . , 



external ear and nose. Conspicuous aggregations, 



modified in form, occur in the eyelids as the Mei- ^w^>y 



bomian glands. 



The smallest sebaceous glands are each little ScSfc 



more than tubular diverticula, dilated at the closed 

 ends. In those of the larger size, the relatively 

 short duct subdivides into several expanded com- 

 partments, which, in the largest glands, may be 

 replaced by groups of irregular alveoli, with uncer- 

 tain ducts that converge into a short wide common 

 excretory passage. 



The structural components of these glands 

 include a fibrous envelope, a membrana propria, and the epithelium, the first 

 two being continuous with the corresponding coverings of the hair-follicle. 

 The epithelium continued into the ducts and alveoli of the sebaceous glands 

 is directly prolonged from the outer root-sheath of the epidermis, where 

 associated with the hair-follicles, or from the epidermis where the hairs 



FIG. 380. Cells from alveoli 

 of sebaceous glands, conspicu- 

 ously showing reticulated cyto- 

 plasm. X 650. 



