210 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



portion. The teeth here also commence to be especially developed. 

 Fishes have a short, simple, wide alimentary canal and stomach, separated 

 by a marked constriction from the small intestine, but the separation of 

 the stomach from the gullet is less marked, being indicated often only by 

 the difference in structure of the mucous membrane ; hence, in these 

 animals regurgitation of food is easy, and is the method which is often 

 employed for the removal of indigestible residue. A form of rumination 

 is also said to occur in certain fishes, the food being regurgitated to the 

 mouth and remasticated by the teeth or pharyngeal 

 bones, as in the carp. In fishes (Figs. 67 and 68) 

 the stomach is usually bent like a siphon, the 

 intestine is straight and short, with but in rare 

 cases any distinction betw r een large and small 

 intestines. There is no distinct ileo-caecal valve, 

 but sometimes a caecum is present. The intestine 

 is rarely supported on a mesentery. 



In the amphibious reptile the type of the 

 alimentary canal is somewhat similar to that of 

 the fish, though the distinction between the large 

 and small intestines is better marked. The oesoph- 

 agus is short, dilatable, and muscular, and the 

 stomach is tubular and may be bent upon itself. 

 A distinction between large and small intestines 



FIG. 67. INTESTINAL CANAL, 

 OP THE STURGEON. 

 (Cam*.) 



BB, pharynx and cul-de-sac of 

 the stomach ; A, pylorus : C, pancre- 

 atic appendices of the pylorus ; below 

 are seen the convolutions of the small 

 intestine terminating in the spiral 

 large intestine. 



FIG. 68. STOMACH OF THE SALMON-TROUT (Carus), 

 SHOWING THE PANCREATIC APPENDICES OF THE 

 PYLORUS AT A. 



is readily made. The influence of the food on the development of the 

 alimentary canal is seen in the long, coiled intestine of the vegetable- 

 feeding tadpole, as contrasted with the short intestine, of the insectivo- 

 rous frog and toad. The crocodile (Fig. 69) has a more complex stomach 

 than any animal lower in the scale. It is a sort of blending of the 

 digestive organ of the cuttle-fish and the bird, having powerful muscular 

 walls, with muscular fibres radiating from a central tendon in a manner 

 very closely similar to that seen in the gizzard of the bird. The 



