352 



STOMACH AND INTESTINE. 



free extremity of the villus: to the contrac- 

 tion of the muscular layer of which it would 

 appear to be chiefly, though not wholly, due. 



The veins (vv,fg. 260.) come off from this 

 network by the gradual union of capillaries 

 in the upper half of the villus, so as to form 

 two or more venous trunks. These are 

 usually about double the width of the corre- 

 sponding arteries : they run at a distance 

 from them ; and often lie rather nearer to 

 the surface of the villus. Below, these 

 trunks become confluent in the single vein 

 of the process ; which, passing vertically 

 downwards, terminates by joining one of the 

 numerous veins belonging to the venous plexus 

 around the orifices of the intestinal tubes. 

 And this latter network also joins that of the 

 viilus by such numerous communications, 

 that the two might almost be regarded as 

 merging into each other. 



The substance which forms the ground- 

 work or basis of the villus resembles, to 

 some extent, that of the gastric mucous 

 membrane ; the morphological consti- 

 tuents of which we have already seen to be 

 indistinct, except at the bottoms of the 

 tubes. It rarely presents any definite struc- 

 ture. Sometimes, however, it is faintly striated. 

 And occasionally this appearance is so marked, 

 as to approach a fibrous character. In this re- 

 spect, it resembles the papillae pf the skin and 

 tongue ; and, especially, those secondary 

 projections which stud the fungi form papillae 

 of the latter organ, the basis of which contains 

 no yellow elastic fibres, but is almost homo- 

 geneous, and often indistinctly granular. 



Mixed with this indistinctly fibrous tissue 

 are numerous delicate cytoblasts or nuclei 

 (b, Jigs. 259, 261, 262, 263.). The larger of 

 these attain the size of coloured blood-cor- 

 puscles ; while the small merge into granules 

 by increasing minuteness. The exact, re- 

 lation of these to the basis of the villus is un- 

 known. Their general effect is to communicate 

 to the whole villus a more or less mottled and 

 granular aspect. This appearance (which we 

 .shall find is increased during the period of 

 intestinal digestion) often obscures, not only 

 the vague fibrillation just alluded to, but the 

 whole of the structures which lie beneath the 

 basement membrane. 



As regards the lacteals of the villi, few 

 anatomical details have been more disputed 

 than those which relate to the commence- 

 ment of the chyliferous absorbents within 

 the substance of these processes. The pro- 

 gress of microscopical research has, how- 

 ever, reduced the controversy within very 

 narrow limits ; and promises at no distant 

 date, to end it by a final decision. At pre- 

 sent, almost all trustworthy observers agree 

 in the statement, that each villus receives 

 by its base a single (perhaps sometimes a 

 double) branch of the lacteal system. It is 

 only as to the further course of this vessel 

 that opinions differ. Many affirm it to be 

 continued up the villus as a single tube, which 

 ends near its apex by a blind and often some- 

 what dilated extremity. Some authorities 



modify this view for the broader villi, by 

 stating the canal to be double either as a 

 single loop, or as a bifid and somewhat tor- 

 tuous tube. While others find that the cen- 

 tral and simple lacteal canal ends by branching 

 into a network of more or less complex cha- 

 racter, like that of the capillaries. 



The first of these statements will at any 

 rate apply to many of the villi. Numerous 

 observers have verified its accuracy for the 

 human subject. And it is not difficult to 

 obtain distinct evidence of its truth in some 

 other Mammalia. Amongst these the sucking 

 Rabbit and Calf are especially suitable for 

 examination. If proper care be taken to 

 examine the chyliferous villi of these ani- 

 mals instantly after death, with the aid of 

 suitable fluids, we may easily convince our- 

 selves of the presence of a single large lac- 

 teal tube, with distinct walls, like that repre- 

 sented in the annexed figure (fig. 26 1.). Such 



Fig. 261. 



b tl d !> 



Two villi, denuded of epithelium, n-it/i the lacteal vessel 

 in their interior, from the Calf. Magnified 350 

 diameters. (After Koelliker.') 



a, limitary membrane of the villus; b, matrix or 

 basis of the same ; c, dilated blind extremity of the 

 central lacteal ; d, trunk of the same. 



single lacteals are generally very large, having 

 a diameter which often amounts to about one- 

 third or one-fourth that of the villus itself; 

 and exhibit a dilated blind extremity, (c,Jig. 

 261.) which nearly doubles their width. In 

 man, according to Frerichs *, they are 

 scarcely more than one-half or two-thirds of 

 this size. 



But it remains to be considered whether this 



* Op. cit. p. 751. 



