252 



MUCOUS MEMBRANES GLANDS 



niinal filaments which enter the epithelial layer and terminate in 

 contact with the secreting cells. The mucous membranes are mostly 

 contained within hollow organs which are subject to alternate col- 

 lapse and distention; hence the membranes are frequently much folded. 

 The deeper portion of the mucous membrane usually contains a more 

 or less well-defined layer of smooth muscle fibers, the muscularis mu- 

 cosce. 



The mucous membranes, as their name indicates, are nearly all moist- 

 ened by a mucus-containing secre- 

 tion. The relative amount of mu- 

 cus which its secretion contains, 

 and consequently the viscidity of 

 the secretion, bears a close physio- 

 logic relation to the intensity of 

 the mechanical irritation to which 

 the membrane is subjected. Thus 

 the mucus-secreting goblet cells 

 of the gastropneumonic membrane 

 are here and there reenforced by 

 numerous mucus-secreting glands 

 of considerable size; these are es- 

 pecially abundant in the oral cav- 

 ity, pharynx, and esophagus, and 

 in the nose, trachea, and bronchi ; 

 in the urinary system even the 

 goblet cells are absent. 



FIG. 254. DIAGRAM OF A Mucous MEM- 

 BRANE HAVING SIMPLE TUBULAR 

 GLANDS. 



a, artery; b-l>, basement membrane; o, 

 connective tissue; (/, duct of the gland, 

 lined by cuboidal cells; E, epithelium of 

 the free surface with clear, columnar 

 cells; G, lumen of the fundus of the gland, 

 lined by granular, serous secreting, col- 

 umnar cells surrounded by secretory 

 capillaries; V, veins. The arteries are 

 striped, the capillaries and veins, black. 

 Nerves are not represented. 



The basement membranes, upon 

 which the epithelium of the mu- 

 cous membranes and the secreting 

 glands is supported, are connective 

 tissue structures. They are some- 

 times formed by interlacing bun- 

 dles of delicate collagenous fibers intermingled with numerous elastic 

 fibers. Frequently, however, they consist of reticular tissue. Basement 

 membranes of this nature have been demonstrated by Mall and his pupils 

 in the mucous membranes and glandular tubules of the stomach, intes- 

 tine, liver, salivary glands, kidney, testis, and thyroid. Occasionally 

 basement membranes are homogeneous or hyaline in structure and pre- 

 sent a more or less clear or glassy appearance. 



