400 STRUCTURE OF THE SMALL INTESTINE. [BOOK II. 



single for some distance, and piercing the muscularis mucosae divides 

 in the submucous tissue into a number of tubes, which subdividing 

 take a twisted course and end in slight enlargements or alveoli. 

 The cells lining both the branching tubes and the alveoli are short 

 cubical cells with an indistinct outline, similar to but, in a fresh 

 condition, more distinctly granular than the cells of the gastric 

 pyloric glands. Bundles of plain muscular fibres, stragglers from the 

 muscularis mucosse, are scattered among the tubes." 



" These glands of Briinner when traced back to the stomach are 

 found to pass gradually into the pyloric glands; traced along the 

 intestine they soon disappear. The ducts of those glands which 

 reach into the duodenum so far as to be found in company with 

 the glands of Lieberklihn and the villi, open into the lumina of the 

 former. It is not clear that any special purpose is served by these 

 glands of Brunner ; an extract of the glands is said 1 to digest fibrin in 

 the presence of an acid 2 ." 



Th Villi " ^^ e v ^ var y * n s * ze anc ^ ^ 01 m * n different animals 



and in different parts of the intestine of the same 

 animal ; each villus, moreover, varies in form at different times ; 

 they may be generally described as having the shape of a flattened 

 finger, but are frequently broader at the free end than at the base ; 

 they have, in man, a length of about 1 mm. and a breadth of from 

 0'2 mm. to '5 mm. 3 " The villi are, like the mucous membrane in 

 general, composed of lymphoid connective tissue covered with a 

 columnar epithelium of somewhat peculiar character, amongst which 

 goblet cells occur, resting on a basement membrane composed of 

 flattened cells. Between the bases of the columnar cells are seen 

 'cells with a relatively small quantity of cell-substance round the 

 nucleus ; these have been taken to be reserve or replacement cells,' 4 

 and in addition to these numerous lymph corpuscles. 



Each villus contains a central lymphatic vessel, or lacteal, which 

 at its upper end is club-shaped and at its base communicates with 

 the lymphatics of the mucous membrane. External to the central 

 lymphatic are fine bundles of involuntary muscular fibres, which are 

 continuous with those of the muscularis mucosse, and the contraction 

 of which will necessarily tend to compress the contents of the lacteal. 

 Still more external, i.e. between the layer of muscular fibres and the 

 basement membrane, are a small artery and vein (conducting blood 

 to and from the villus and communicating with larger vessels in the 

 submucous tissue) and a plexus of capillaries establishing a communi- 

 cation between them. The space between the basement membrane 

 and the central lacteal is occupied by adenoid tissue, i.e. by a retiform 

 or reticular connective tissue, the meshes of which are occupied by 

 leucocytes. 



1 P. GrUtzner, Pfliiger's Archiv, Vol. xn. (1876), p. 290. 



2 Foster, op. cit. p. 449. 3 Foster, op. cit. p. 445. 

 * Ibid. p. 447. 



