GLANDS 257 



Many of the serum-secreting cells contain minute inlracellu/nr c 

 which connect with a network of intercellular passages about the cell. 

 The intercellular canaliculi may, on the one hand, open into the glandu- 

 lar lumen, or they may communicate with the tissue spaces of the tunica 

 propria. This system of intracellular and intercellular canaliculi may 

 thus serve either as a system of nutrient channels or as a network of 

 secretory capillaries by which the secretion is conveyed from the interior 

 of the secreting cells to the lumen of the gland or even to the duct 

 system. Nutrient and secretory canaliculi of this nature have been 

 demonstrated in the secreting cells of the liver, cardiac glands of the 

 stomach, salivary glands, pancreas, adrenal, and epididymis, but they 

 are not by any means confined to the actively secreting cells, for they 

 have been found in the cells of bladder epithelium (Holmgren) and 

 are highly developed in the nerve cells (Holmgren, Golgi, et al.). 



DESCRIPTION OF HISTOLOGIC TYPES 



Simple Tubular Glands. Simple tubular glands occur in the mu- 

 cous membrane of the small and large intestine as the crypts of Lieber- 

 kiihn or intestinal glands. In shape these glands resemble a test-tube. 

 They form straight tiibules which open on the free surface of the mem- 

 brane, are of approximately equal caliber throughout, and at their deeper 

 end terminate in a blind extremity. The tubules are lined with epi- 

 thelium and are embedded in a thin vascular tunica propria. Their 

 epithelium includes the usual columnar and goblet cell types, the latter 

 being more abundant near the mouth of the gland. Near the blind 

 extremity are certain granular cells, the granules of some of which are 

 slightly basophilic : other cells possess coarse granules which are highly 

 acidophil, as demonstrated by Kultschitsky (Arch. f. mik. Anat., 1897) 

 in the intestinal glands of the dog, an observation which is easily cor- 

 roborated for the simple tubular glands in the small intestine of man. 



Convoluted Tubular Glands. Convoluted tubular glands occur as 

 the sweat glands of the skin, the ceruminous glands of the ear, and the 

 glands of Moll in the eyelids. The above are typical simple coiled 

 glands. Certain other glands, which are less typically coiled but are 

 more or less convoluted near their blind extremities and are frequently 

 branched, are also to be included under this type. Such glands are the 

 pyloric glands of the stomach, and the small mucous glands of the 

 oral and nasal cavities, pharynx, larynx, trachea, bronchi, and esophagus. 

 Some of these glands, and especially those of the pyloric end of the 

 17 



