186 



ANIMAL PHYSIOLOGY. 



[LESSON 52. 



803. A figure of filiform papillae of the Dog, minutely injected, 

 is given in Fig. 297, and also of two circumvallate papillae in Fi<r. 

 298 ; in both instances the terminal nervous loops accompany the 

 capillaries, and necessarily impart great sensibility to these organ?. 

 The circuinvallatae are very small in the Dog. 



FIG. 297. FIG. 299. 



FIG. 293. 



Circumvallate papillae 

 of the Dog. 



papilla-, Tongue, Dog. 



Mucous membrane of Stomach, 

 Dog. 



FIG. 



804. The structure of the mucous membrane of the stomach of a 

 Dog is highly interesting, as will be seen by reference to the accom- 

 panying figure of it (Fig. 299). Here the gastric cavities are beau- 

 tifully formed, their cell-walls consisting of a single, tortuous capil- 

 lary blood-vessel, and the deep-seated vessels which surround the mu- 

 cus-tubes are well shown. / 



805. The line of demarcation which separates one tissue from 

 another is always remarkably abrupt. Some (theoretical) physiolo- 

 gists hold, that the change of one form of tissue into another is so 

 very gradual as to become quite insensible ; an opinion entirely op- 

 posed to fact : for example, the structure of the stomach continues 



half way through the pyloric valve, the 

 other half of it being duodenum, as will 

 be seen in Fig. 300, from the Dog. It 

 is quite true that the stomach exhibits 

 papillae, in addition to its gastric cells, 

 prior to the commencement of the pyloric 

 valve, and within the stomach a fore- 

 shadowing of the important tissue here- 

 after to become, not the exception, but 

 the rule; they do not extend, however, 

 to the pylorus, and are more usual in 

 man than in the stomach of domestic animals. So, too, as regards 

 the ilio-caecal valve, which forms the junction of the ileum with the 

 caecum and colon ; the structure of the small intestine remains in- 

 tact half through the valve, when the caecum abruptly joins it. An 



Junction of stomach and duo- 

 denum, Dog. 



