326 



EPITHELIAL AND ENDOTHELIAL TISSUE. 



variety is the currant-shaped racemose gland, in which the -acini 

 encircle the longitudinal duct, as in the Meybomian glands. 



A prolongation of the epithelium in the longitudinal, or rather 



in a vertical, direction is 

 termed a simple tubular 

 gland, such as the pepsine, 

 the intestinal, and the utric- 

 ular glands. Repeated ram- 

 ifications of the tubules re- 

 sult in the formation of 

 compound tubular glands ; 

 for example, the urinifer- 

 ous and seminiferous tub- 

 ules. Another sub-variety 

 of tubular glands may orig- 

 inate by the coiling of the 

 tubule. Examples of these 

 coiled tubular glands are 

 the sweat and ceruminal 

 glands. 



There are transitions 

 between these two princi- 

 pal varieties, when the acini 

 are slightly elongated, as 

 in the prostate, in the mu- 

 cous, or Littre's glands of 

 the urethra, and the mu- 

 cous or Brunner's glands 

 of the duodenum. 



According to this defi- 

 nition, only epithelial 

 i. #., secreting formations 



glands: a, the simple pouch ; b, the branching race- 

 mose form ; c, the branching currant form. 



The series T exhibits the varieties of tubular 

 glands : a, the simple tube ; &, the compound branch- 

 ing tube; c, the coiled tube. 



FIG. 141. DIAGRAM OF GLANDS. 



The series A exhibits the varieties of acinous 



can properly be desig- 

 nated glands, and all the 

 so-called lymph-glands, the 

 adenoid lymph-ganglia, the 

 spleen, the thymus, and the thyroid body should be excluded 

 from the glandular system, as they are not secreting, neither 

 are they epithelial in structure. 



The epithelia rest upon a delicate hyaline layer of connective 

 tissue, which bears the superfluous name of a " membrana pro- 

 pria." It is of varying width, and is identical with the " base- 



