h2 DIGESTIVE ORGANS, ITC. 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 Platalea 
and Hurynorhynchus (spatulate) to the “arch” of Numenius, the 
“scissors” of Rhynchops, the “ wedge” of Picus, the big rounded 
feature of the Pscttac?, 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 
Phoenicopterus, Prion and Anastomus being especially remarkable. 
Teeth were probably lost by Birds before Tertiary times, but were 
possessed at least by Archaeopteryx, Hesperornis and Ichthyornis. 
The so-called “ ege-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 with 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 obtaiming nutriment. To this follows the 
cullet (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, often 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 
