322 



STOMACH AND INTESTINE. 



composition. These changes seem to be the 

 result, partly of putrefaction, partly of a self- 

 digestive process. And since we scarcely 

 ever have any opportunities of examining 

 the perfectly healthy stomach of Man imme- 

 diately after death, we are compelled to lay 

 unusual stress upon the structure seen in 

 those of the higher Vertebrate animals which 

 approach most nearly to the human conforma- 

 tion of this organ. 



Among the various domestic Mammalia 

 most accessible for such purposes, the struc- 

 ture and habits of the Dog render its sto- 

 mach, in many respects, one of the best we 

 can select for examination. 



In this animal, the tubes of the cardiac 

 extremity (u, Jig. 248.) begin on the free or 



Fiv. 2-17. 



Mucous membrane from the middle of the Dog's 

 stomach, as seen from the free surface. Magnified 

 150 diameters. 



a, ridges which intervene between the primary 

 tubes, covered by columnar epithelium; b, primary 

 tubes, lined by similar columnar cells ; c, secondary 

 tubes, given off from the preceding, and lined, at 

 their commencement, by similar cells; d, central 

 calibre, or cavity, of a secondary tube. 



cavitary surface of the organ, by apertures 

 which form the intervals of a kind of net- 

 work of ridges. These apertures are polygonal, 

 or irregularly six-sided, and the tube into 

 which each soon merges has a diameter that 

 is very little less than the distance between 

 the ridges; on an average about ^mrth f 

 an inch. The tube now proceeds down- 

 wards for a short distance, before bifur- 

 cating into two smaller tubes. And each of 

 these again divides at a further stage of its 

 descent. In this manner, what was at first 

 a single large cylinder, ends as a bundle of 

 about four or five small tubes, which are col- 

 lectively enclosed in a portion of matrix 

 thicker than that occupying their interstices. 

 At the pyloric extremity of the organ, the 

 tubes (A,^ftg.24:S.} commence by apertures,which 

 have a diameter twice as great as those seen 

 in the cardiac region, and from hence they 

 pass vertically downwards for some distance, 



with a simple cylindrical form. All the ter- 

 minal branches of these long pyloric tubes 

 are for the most part given oft' at nearly the 

 same height, so that they constitute only 

 one-sixth, or thereabouts, of the whole thick- 

 ness of the mucous membrane, instead of 

 about five-sixths, as in the cardiac extremity. 

 In both the above regions, however, the num- 

 ber of these terminal tubes is rarely less than 

 three, or more than six. Their diameter is 

 generally about one-third that of the larger 

 and simple tube from which they originate. 

 And the total bulk of the bundle which they 

 form, as seen on transverse section, is as 

 nearly as possible equal to that of the primary 

 tube. 



But these differences in the width and 

 ramification of the cardiac and pyloric tubes 

 are accompanied by a much more remarkable 

 and important contrast in the form, size, and 

 arrangement of their respective contents. 



The whole of the pyloric tube (A,/. 248.) 

 is occupied by a single layer of columnar epi- 

 thelium, the cylindrical or slightly prismatic 

 cells of which are placed vertically to the 

 basement membrane, and contain a very dis- 

 tinct nucleus near their attached extremity. 

 The only difference offered by these cells 'in 

 the terminal branches of the tube is, that they 

 are shorter in proportion to their width, and 

 enclose darker and more granular contents. 



Fig. 248. 



Tunes from the cardiac and pyloric regions of the 

 Day's stomach, to show the contrast of their struc- 

 tures. Magnified 60 diameters. Altered from 

 Koelliker. 



A. p3'loric tube ; a, primary tube ; b, three second- 

 ary tubes. B. cardiac tube ; a, primary tube lined 

 by columnar epithelium ; b, two secondary tubes ; 

 c, four terminal branches containing large oval 

 cells. 



