342 



SAUEOPSIDA (birds). 



never contains teeth : it is variable in appearance, and is used 

 for eating the prey and food generally, for prehension, and 

 in some as an organ of touch. The hase of the upper bUl 

 is often surrounded hy a circle of skin devoid of feathers, the 

 "cere.'' The tongue is mostly hard and horny, and is supported 



by the hyoid bone. The digestive 

 tract consists of a long gullet or 

 oesophagus (fig. 179, Oe), which 

 has a sac-like dilatation in front 

 of the " merry - thought,'' the 

 crop (C). This crop is seen in 

 carnivorous and graminivorous 

 birds. Here the food is retained 

 prior to the gastric digestion 

 The oesophagus is followed by 

 the iiroventriculus , which is the 

 true stomach in which gastric 

 digestion takes place. This fiist 

 stomach corresponds with the 

 cardiac end of the mammal's 

 stomach. The pyloric end is 

 represented by the "gizzard" 

 ((?), a large extremely muscular 

 cavity situated below the hver. 

 There are two distinct types of 

 this grinding stomach : in rap- 

 Oc (Esophagus ; c crop ; s, proven- torial birds it consists of a 



tnculus ; (r, gizzard ; D, duodenum ; St, 



small intestine ; Cae, cicca ; /, junction simple membraUOUS SaC, but W. 



of cteca ; ii, rectum; CL, cloaca; .4, ^ 



anus; L, liver; Gh, gall bladder; 0, cjraminivorous birds, which eat 



right lobe of liver ; P, pancreas. ^ , 



hard and not easily digested 

 food, the gizzard consists of a thick muscular cavity which is 

 lined by a hard epitlielium. Ey the muscular action of the walls 

 of the gizzard the food is ground up against the horny walls. 

 In all birds we find in this second stomach small stones, cinders, 

 and grit. These aid in the trituration of the food. They are 



Fig. 179. — Alimentary Canal of 

 Fowl. 



