NORMAL HISTOLOGY. 



as in many pyloric or uterine glands, to the intricate arrangement 

 of the tubules of the kidney or the testicle. 



Simple saccular glands do not occur in the higher animals, but 

 are conspicuous in the lower types, as in the integument of am- 

 phibians. Compound saccular, or racemose, glands, on the 

 other hand, are represented in man and mammals by such important 

 organs as the pancreas and the salivary glands. 



In the least complex type of gland, the simple tubular, the two 

 fundamental parts of all glands are distinguishable in their primi- 

 tive form : these are the deeper actively secreting portion, the fundus, 

 and the superficial division, or duct, through which the products of 

 the secreting cells escape. Dilatation of the fundus of the primitive 

 type produces the simple saccular gland ; division of the fundus and 

 of part of the duct originates the compound tubular variety ; repeated 

 cleavage and subdivision of the duct, with accompanying expansion 

 of the associated terminal tracts, lead to the production of the com- 

 pound saccular, or racemose, type. 



The tubular glands may exist as perfectly straight cylindrical 

 depressions ; more usually, however, the tubes are somewhat wavy 



or tortuous : when the torsion of the fundus 

 FIG. 164. reaches its highest expression, such modi- 



fications as the coiled sweat-glands result. 



Glandular epithelium is the direct de- 

 rivative of the cells covering the adjacent 

 mucous membrane, so modified and special- 

 ized as to adapt it to the requirements of 

 the several parts of the gland. In simple 

 tubular follicles the cells of the adjacent 

 free surface pass into those lining the neck 

 of the gland with little change ; cells of the 

 increased size and spherical form become 

 more pronounced towards the fundus, where 

 the elements assume the characters of se- 

 creting epithelium. The cells lining the 

 upper part of the duct of such glands not 

 infrequently exhibit a distinctly imbricated 

 arrangement ; this is well seen in the peptic 

 glands. 



The greater complexity of the racemose 

 glands resulting from the system of freely 

 branching excretory tubes renders the recognition of several parts 

 desirable. These are, towards the ducts, proceeding irom the ter- 

 minal compartments, the alveoli or acini, the intercalated or 

 intermediate tubules, the intralobular tubes, the interlobular 



Tubular glands : A, simple tubu- 

 lar crypt from human small intes- 

 tine; B, compound tubular gland 

 from pyloric end of human 

 stomach. 



