ORGANS OF THE BODY. 



485 



one against the other (fig. 471, &), so that, according to Krauze's 

 estimate, about from 50 to 90 spring from 1 Q mm. in the jejunum, and 

 duodenum, and in the ileum from 40 to 70, giving 

 for the whole extent of the small intestine, accord- 

 ing to his calculation, 4,000,000. Their height 

 varies from 0*23 to 1'13 mm. and upwards. 

 Their breadth also differs, naturally, according to 

 their form. Transverse sections show them to be 

 either cylindrical or leaf-shaped. 



All these villi are clothed with peculiar col- 

 umnar epithelial cells, already referred to (p. 147), 

 which present on their free surfaces a thickened 

 border, perforated by pores or fine canaliculi (fig. 

 472, a). 



Between these cells (fig. 473, b) may be ob- 

 served not unfrequently distributed with toler- 

 able regularity those "goblet cells" which have 

 been already brought before our notice ( 93). 

 In number they vary with the species and the 

 individual. 



We also encounter here, as in the stomach, 

 small roundish structures lying between the in- 

 ternal extremities of the columnar epithelium 

 cells. These may be regarded as destined to 

 replace the latter as they successively perish. 



Under the epithelial layer we next come upon 

 the framework of the structure in the form of 

 reticular connective - substance with entangled 

 lymphoid corpuscles and nuclei in some of the 

 nodal points of its not unfrequently long meshed network. 



The recognition of the true nature of the surface of the villus is 

 attended with considerable difficulty. Nevertheless, we may see that 

 here also it preserves the same retiform character, although the bands 

 may in many instances become broader and flatter, and the interspaces 

 between them decrease in size until they 

 become merely small apertures, so that the 

 effect almost of a homogeneous mem- 

 branous limiting layer may be given. 



This tissue of the villi is traversed in 

 the first place by a vascular network (?;), 

 next by a lymphatic canal (d), occupying 

 the axis of the structure, and lastly, by 

 delicate longitudinal bundles of unstriped 

 muscular fibres (c). For the discovery of 

 the latter we are indebted to Briiclke, although anterior to his researches 

 on tlie subject, distinct contractility had been recognised in the intestinal 

 villi in the living or recently killed animal, producing numerous wrinkles 

 on the surface of the process .(Lacauchie, Gniby, and Delafond). These 

 bundles of muscle fibres may be traced down through the mucous mem- 

 brane into the muscularis of the latter. 



The vascular netivorks of the intestinal villi (figs. 474, 475) occupy 

 invariably the peripheral portions of the latter, and are supplied in the 

 smaller mammalia each by a small arterial twig or pair of the same (a), 



Fig. 472, An intestinal villus 

 (after Leydig) . a, columnar 

 epithelium with thickened 

 border or cuticular mem- 

 brane ; b, capillary network ; 

 c, longitudinal muscular 

 bundles; d, axial chyle 

 radicle. 



Fig. 473. Epithelial cells from a human 

 intestinal villus (after Schulze). a, 

 goblet cells; 6, ordinary elements. 



