VERTEBEATA AYES. 



37 



in the emeu and cassowary, the hind toe is wanting or 

 rudimentary. The African ostrich has only two toes. 

 The hind toe, when present, has two, the innermost three, 

 the next four, and the ff 3 ] 



third five phalanges. 



35. Digestion. 

 Birds are destitute of 

 teeth. The mandibles 

 or jaws are sheathed 

 with a horny substance 

 forming a beak. They 

 are provided with sali- 

 'vary glands, which 

 are much smaller than 

 in mammals. The food 

 passes through, a long 

 gullet into a pouch 

 called the crop, where 

 it remains for some 

 time. This crop, which 

 may be considered an 

 expansion of the gul- 

 let, is wanting in some 

 birds. It is then trans- 

 ferred to the true di- 

 gestive stomach, where 

 it is mixed with the 

 gastric j nice. Having 

 been imperfectly mas- 

 ticated, owing to 



absence of teeth, the cular waif of gizzard; g, duodenum; ' h', small 



f^ J CL 1 xi intestine ; ii, intestinal cceca ; Jc. commence- 



lOOd, after leaving tllO ment O f large intestine; l t cloaca; w, liver; 



true Stomach, is COn- ', pancreas. 



veyed to a muscular bag, called the gizzard, provided with 

 a rough horny lining, which, assisted by gravel swajfewed 

 by the bird, reduces it to a pulpy mass. This kind of gizzard 

 is found in grain-eating birds only. In birds of prey which 

 live upon flesh its coats are thinner, and it is a much less 



FlG> IO.-DIGESTIVE APPARATUS OF TUB 

 COMMON HEN. 



a, the lower part of the oesophagus ; 6, crop ; 

 Mr ' ue digestive rtomach; d, gizzard; e, m us- 



