266 



PHYSIOLOGY 



f'HAl'. 



are large valvulae conriiventes and the villi are long and very 

 numerous. The visible surface of measurement of the small 



y- 



Fio. 87. Cross section of a villus of cat's intestine. Highly magnified. (E. A. SehafiT.) 

 e, columnar epithelium ; r/, goblet-cell with mucus partly exuded ; Z, lymph-corpuscles betwrrn 

 the epithelium cells ; b, basement-membrane ; c, blood corpuscles ; m, section of plain muscular 

 fibres ; i-l, central lacteal. 



intestine extends in the adult to some half a square metre. But 



the many folds of the valvulae con- 

 niventes, and extensive inflexions and 

 projections of the mucous coat of the 

 villi, increase the true surface of this 

 part of the mucous membrane to 

 about 10 square metres. The chyme 

 is distributed over this vast absorbing 

 surface, so that absorption the main 

 function of the epithelium that clothes 

 the villi as well as the solitary and 

 agminated glands scattered over the 

 small intestine is greatly ^ facilitated. 

 The villi, as the chief organs of 

 absorption, claim special attention. 

 They vary in length from 0'5-0'7mm., 

 are larger and more numerous in the 

 duodenum and jejunum, and diminish 



j nlrm V, PT i n f}-, p I'lpnni 



m 



to KrailSC, each Square 

 . . 



millimetre OI the jejunum Contains 



-i A 1 O -P^V '1 Oil /" fl ^ 



lU-lo, OI tile 11611111 O-14. Ull 1116 



Kr, a i c n f flTie pilpnlTHnn rhp tnral 

 DaS1 



number of villi in the whole of the 



small intestine may be taken as four 

 to five millions, and each square centimetre of the apparent surface 

 of the intestine gains about twenty-three times in area from the 



FIG. 88. Injected lacteal vessels in two 

 villi of human intestine. (Teichmann.) 

 100 diameters. The lacteals are filled According 

 with white substance; the blood- 

 vessels with dark, a, b, lacteals, single 

 in one villus, double in the other; 

 r, horizontal lacteals, communicating 

 with those of the villi; d, blood- 

 vessels which consist of small arteries 

 and veins with capillary network 



