266 



BRANCH CHORDATA 



The Digestive System. The mouth is devoid of teeth in exist- 

 ing birds. Extinct birds (see Figs. 209 and 210) had teeth (see 

 Geology). Can the student see any reason why birds have lost 

 their teeth? The beak (Fig. 217) is very strong in birds of 

 prey, such as the eagle and hawk. The mouth opens into the 



Fig. 217. Forms of beaks (a, b, c, d, k, after Xaumann; g, i, m, o, regne 

 animal; /, from Brehm) : a, Phcenicopterus antiqiiorum; b, Platalea leucorodia; 

 c, Emberiza citrinella; d, Turdus cyanus; e, Falco candicans; f, Mergus 

 merganser; g, Pelecanus perspicillatus ; h, Recumrostra arocetla; i, Rhyn- 

 chops nigra; k, Columba livia; I, Balcniiceps rex; m, Anastomos coromande- 

 lianus; n, Pteroglossus discolor; o, Mycteria senegalensis; p, FalcineUies 

 igneus; q, Cypselus apus. (After Glaus.) 



esophagus, which opens into the large crop, in which the bird rap- 

 idly stores its food, which is passed on to the glandular stomach 

 or proventriculus. It is then passed to the muscular gizzard, 

 where with the aid of gravel and other hard substances, the food 

 is ground fine. The spleen is a small, red ovoid body at the right 



