148 



PHYSIOLOGY F-'OR BEGINNERS 



a small amount of a special kind of connective tissue between 

 them. The tubular glands are lined by a single layer of cubical 

 or cylindrical cells. They are called the crypts or glands of 

 Lieberkiihn, after the man who first described them. In 

 respect to its epithelium, and its glands, the mucous membrane 

 of the small intestine is similar to that of the stomach, but it 

 differs from it in not being level at the surface. The mucous 

 membrane of the small intestine between the glands is 

 thrown up into small finger- like processes, placed thickly 



together, so that the internal 

 surface is closely beset with 

 them, and this gives the sur- 

 face an appearance to the 

 naked eye not unlike that of 

 velvet. These processes are 

 called villi. Each villus is 

 club-shaped and is covered 

 entirely by the epithelium of 

 cylindrical cells. Under the 

 epithelium the substance of 

 the villus is made up of a kind 

 of fine connective tissue which 

 is continuous at the base of the 

 villus with the similar tissue 

 lying between the tubular 

 glands. In this connective 

 tissue there are numerous 

 blood-vessels, one or more 

 small arteries entering each 

 FIG. 66. Two villi. Highly magnified, villus, and breaking up into 

 e, Epithelium; /-. v, blood-vessels ; /, lacteals. capillaries, which are collected 



again into one or more small 



veins which leave the villus to join with other veins in the wall of 

 the intestine. In the connective tissue at the centre of each 

 villus is an elongated, and sometimes branched space, which is 

 the beginning of a lymphatic vessel, and this, passing out of the 

 villus at its base, unites with other lymphatics in the wall 

 of the intestine, whence it may be traced to the thoracic duct. 

 The lymphatic vessels which thus start in the villi are called 

 lacteals. 



