CHORDATA 



335 



slits become closed as the embryo develops. Above the 

 Amphibia they never bear gills. 



The esophagus is a narrow muscular tube of varying length 



Fig. 162. Stomach of Dog (A) and of Ratj(£). c, cardiac portion; p, pyloric portion; 0, 



esophagus; *, intestine. 



Fig. 163. Diagram of the stomach of a ruminant, o, esophagus; r, rumen or paunch; r^.. reticu- 

 lum, or honeycomb; p, psalterium or manyplies; a, abomasum or rennet; f, intestine. 



Questions on figures 162 and 163. — Taken as a series, what is illustra.ted by the 

 three diagrams? What do the arrows indicate? What is known of the function 

 of the various portions of the ruminant stomach ? 



leading to the stomach. In birds an enlarged portion of it 

 (the crop) may serve for the temporary storing and softening of 

 the food. 



