ADAPTATIONS IN WARM-BLOODED ANIMALS 157 



ments. The first and largest is called the rumen, and into 

 this the grass mixed with saliva passes without mastication 

 as it is eaten. From this rumen the food is passed into a 

 second compartment 

 with a honeycombed 

 wan and called the 

 reticulum. After the 

 grazing is over the 

 food is returned to 

 the mouth from this 

 reticulum in the form 

 of boluses or. round 

 balls called the cud. 

 This cud is then thor- 

 oughly masticated by 

 the molars and finally 

 swallowed again. This 

 time it passes directly 



into a third compartment called the psalterium, which is 

 ridged, and strains the food into the fourth compartment, 

 the abomasum or rennet stomach. In this abomasum the 

 actual digestion takes place, and here is secreted the gas- 

 tric juice. Such an arrangement as this is very evidently 

 an adaptation to compensate for the greater difficulty of 

 digestion of such food as grass and hay; but it is to be 

 noted that in none of these cases is the purpose and 

 general method of digestion essentially different. 



In all, the various structures arc working to one common 

 end, namely, the transforming of food into soluble matter. 

 And the ultimate method employed is the action of fer- 

 ments or enzymes secreted by cells located in the walls or 

 connected with the digestive tract. 



Fig. 57 — Stomach of a slieep (ruminant) ; e, 

 esophagus ; Ru, rumen ; R, reticulum ; Ps, 

 psalterium ; A, abomasum ; P, pylorus ; Z>, 

 duodeuuni. 



