254 OP FOOD AND THE DIGESTIVE PROCESS. 



muscular and tendinous walls ; such as we find in the grain-eating Birds, 

 and many Insects, and in certain Molluscs and Polypes. But where 

 the food is already composed of very minute particles, or is received in 

 a liquid state (as in the case of those animals which live upon the juices 

 of others), or is easily acted on by the gastric juice, no such preparation 

 is requisite. 



446. Before the food reaches the true digestive stomach, it is some- 

 times delayed in a previous cavity, in order that it may be macerated 

 in fluid, and may be thoroughly saturated with it. This is the purpose 

 of the crop of Birds, and of the first stomach of Ruminant animals. 

 When this incorporation with fluid is not effected before the food is sub- 

 jected to the triturating process, it usually takes place concurrently with 

 it ; and in those animals which reduce their food in the mouth by the 

 process of mastication, there is a special secretion of fluid into that 

 cavity, for this purpose ; this fluid is termed Saliva, and the act by 

 which it is incorporated with the food is termed insalivation. The 

 mechanical reduction of the aliment, and its incorporation with fluid, 

 constitute, as we shall hereafter see, a very important preparation for 

 the true digestive process. 



447. This process, among the higher animals, takes place exclusively, 

 or nearly so, in the stomach ; the form of which varies with the charac- 

 ter of the food. When this is of a nature to be easily acted on by 

 the gastric fluid, the stomach is a simple enlargement of the alimentary 

 canal, almost in the direct line between the oesophagus and the intestinal 



Fig. 74. 



A vertical and longitudinal section of the Human stomach and duodenum, made in such a direction as to 



include the two orifices of the stomach. 1. The oesophagus; upon its internal surface the plicated arrange- 



at of the cuticular epithelium is shown. 2. The cardiac orifice of the stomach, around which the fringed 



border of the cuticular epithelium is seen. 3. The great end of the stomach. 4. Its lesser or pyloric end. 



5. The lesser c.urve. 6. The greater curve. 7. The dilatation at the lesser end of the stomach, which has 



ceived from mill* the name of antrum of the pylorus. This may be regarded as the rudiment of a second 

 omach. 8. The ruga} of the stomach formed by the mucous membrane : their longitudinal direction is 



>wn. 9. The pylorus. 10. The oblique portion of the duodenum. 11. The descending portion. 12. The 

 pancreatic duct and the ductus communis choledochus, close to their termination. 13. The papilla upon 

 which the ducts open. 14. The transverse portion of the duodenum. 15. Thejcommencement of the jeju- 

 num. In the interior of the duodenum and jejunum, the valvulse conniventes are seen. 



tube ; so that there is little provision for the delay of the food in its 

 cavity. But when the aliment is such as to be less easily reduced, and 



