84 



COMPARATIVE ZOOLOGY. 



In Birds, the length of the alimentary canal varies with 

 their diet, being greatest in those living on grain and fruit. 

 The gullet corresponds in length with the neck, which is 

 longest in the long-legged tribes, and in width with the 

 food. In those that swallow large fish entire, the gullet 

 is dilatable, as in Snakes. In nearly all Birds, the food is 

 delayed in some cavity before digestion : thus, the Pelican 

 has a bag under the lower jaw, and the Cormorant has a 



capacious gullet, 

 where they store 

 up fishes; while 

 those that gorge 

 themselves at in- 

 tervals, as the 

 Vulture, or feed 

 on seeds and 

 grains, as the Tur- 

 key, have a pouch, 

 called the crop, 

 developed near 

 the lower end of 

 the gullet. 45 The 

 Ostrich, Goose, 

 Swan, most of 

 the Waders, and 

 the fruit or in- 

 sect eating Birds, 

 which find their food in tolerable abundance, and take it 

 in small quantities, have no such reservoir. Pigeons have 

 a double crop. 



In all Birds, the food passes from the gullet into the 

 proventriculus, or stomach proper, where it is mixed with 

 a "gastric juice" secreted from glands on the surface. 

 Thence it goes into the gizzard, an oval sac of highly 

 muscular texture, and lined with a tough, horny skin. 4 ' 



FIG. 49. Stomach of the Crocodile: , muscular fibres ra- 

 diating from a ceutral tendon, b; d, commencement of 

 duodenum ; c, oesophagus ; /, intestine. 



