berknhn. 



102 GLANDS. 



mary gland, alone belong to tlie second class. We 

 shall see hereafter that these considerations are also 

 equally applicable to tubular glands. 

 of Lie- SECTION 2d. TUBULAR GLANDS. The most simple 

 form of tubular glands are those of Lieberkuhn, 

 which, as is well known, are thickly scattered 

 throughout the whole extent of both the small and 

 large intestine. They are simple straight tubes, one 

 end of which opens upon the free surface of the intes- 

 tinal mucous membrane, whilst the other, slightly 

 enlarged into a bulbous sac, is imbedded in the 

 deeper portion of this same membrane (PL XXVI. 

 fig. X.). Their mean diameter varies from aVth to 

 aVth of a line. Each follicle is. composed of a struc- 

 tureless basement membrane, on the outer surface of 

 which the blood-vessels belonging to the intestinal 

 glands ramify, whilst within it is lined by a single 

 layer of cylindrical epithelial cells, which are arranged 

 very regularly around the cavity of the tube (PL 

 XXVI. fig. XI. 1, 2). The cavity varies from lioth 

 to T^rth of a line in diameter. 



Development. The development of these glands is effected at the 

 expense of the epithelial lamina of the intestine, 

 which is protruded like the finger of a glove in the 

 form of a tube. They will be hereafter more fully 

 examined in connexion with the intestinal mucous 

 membrane. 



The glands which secrete pepsin, found near the 

 cardiac orifice of the stomach, and its mucous follicles, 

 situated near the pylorus, are nothing more than 

 compound follicles of Lieberkuhn. They are com- 

 posed of from two to six single tubes, siinilarlto those 



