143 



THIRTEENTH LECTURE. 



trance of the biliary duct, becoming more scanty further 

 downwards. The mammalia show numerous variations. 



The size varies in man from 0.25 to 2 mm. The acini ap- 

 pear rounded, elongated, sometimes regularly tube-like (0.56 

 too. 14 mm.) The duct and gland body have the same cover- 

 ing of low cylindrical, pale and irregular cells. If I am not 

 mistaken, the Brunonian gland stands in the middle, between 

 the ordinary racemose mucous gland, the gastric-mucous 

 gland and the serous gland. Concerning the secretion we 

 know very little. 



Isolated lymphoid follicles (solitary glands) may occur 

 throughout the entire small intestine. These, as well as the 

 aggregated lymphoid follicles (the Peyer's plates) have already 

 been mentioned in the eleventh lecture. 



We have already mentioned that the Lieberkuhnian tubu- 

 lar glands have an elongated net-work of blood-vessels. From 

 it arise, and to it return, the afferent and efferent vessels of 

 the intestinal villi, which form the looped net-work (Fig. 95, b). 

 The lymph or chyle vessels of the intestinal villi, having 



descended into the mucous 

 membrane, likewise form a net- 

 work, very much more incom- 

 plete it is true, of wider tubes. 

 Our Fig. 109 (a, b, c, k, to the 

 left) may represent this toler- 

 ably. During the resorption 

 of the chyme, its fat, in a con- 

 dition of the finest division, 

 penetrates first the body of 

 the cylindrical epithelium ; it 

 then enters a wall-less passage 

 through the reticular connective 

 substance of the villi, and, at 

 last, the csecal chyle canal (Fig. 

 1 39) occupying the axis of the latter.  ' Preformed passages " 

 for this process of wandering have frequently been searched 

 for, it is true, and they have often been thought to be found, 



Fig. 139. — The very slender intestinal 

 villus of a kid, killed during digestion, with- 

 out epithelium, and with the lymphatic ves- 

 sel tilled with chlye, in the axis. 



