I 2 DIGESTIVE ORGANS, ETC. chap. 



those with none. The narrow slit-like or entirely closed nostrils 

 of the Steganopodes should also be mentioned. 



The form of the bill varies from the " spoon " of Platalca 

 and EiirTjnorhynchus (spatulate) to the " arch " of Numcnius, the 

 " scissors " of RhyiicJwps, the " wedge " of Picus, the big rounded 

 feature of the Psittaci, and so forth ; but for details the characters 

 of the several Families must be consulted, as also for helmets, 

 shields, horns, knobs, and peculiarities due to the elongation,, 

 distorting or crossing of the mandibles. These, too, are often 

 notched, serrated, lobed or '"' festooned," or emarginate (slightly 

 indented) ; the curious transverse serrations or lamellae of the 

 beak in Anseres, and the somewhat similar sifting- apparatus in 

 P/iocnicopterus, Prion and Anastomus being especially remarkable. 

 Teeth were probably lost by Birds before Tertiary times, but were 

 possessed at least by Arcliaeoptcryx, Hesperornis and Ichthyornis. 

 The so-called " egg-tooth " of embryos is merely a calcareous pro- 

 tuberance on the upper surface of the bill, which is cast after 

 being used to crack the shell. 



9. The organs of deglutition and digestion begin w4th the 

 tongue, which is subject to much variation of structure, accord- 

 ing to the different groups of Birds, and is of course correlative 

 with their habits. It has little connexion with taste, though 

 often of assistance in obtaining nutriment. To this follows the 

 gullet {oesophagus), which in many cases has an enlargement 

 forming the crop (ingluvies), wherein the food may be tempor- 

 arily retained before passing into the stomach, the last-named 

 always having an antechamber (proventriculus) where digestion 

 is largely accomplished, in front of the gizzard (ventriculus). This 

 has frequently strong muscular walls, and its action is often 

 assisted by the mechanical process of comminution performed by 

 stones, grit or sand, swallowed for that purpose. The stomach is 

 succeeded by the intestines, which in most cases have a pair of blind- 

 sacs (caeca) attached to them, Qften acting as aids to digestion, 

 though these are not always functional, and are absent in many 

 Birds, while in others they attain a very large size, their con- 

 dition being in consequence of some importance as a systematic 

 character. 



10. The organs of voice in Birds have long attracted special 

 interest from the loud cries which some utter, and the melody 

 with which others are gifted. Setting aside the part played by 



