20 ORGANS OF DIGESTION. 



observe elastic membranes stretched in its interior and a great 

 number of muscles, designed to move the solid pieces that com- 

 pose it; but in those birds that do not modulate sounds, its 

 structure is much more simple. 



25. The organs destined to perform the various functions of 

 nutrition are nearly the same as those in the mammalia. 



26. The apparatus of digestion in the class of birds presents 

 the greatest uniformity of structure : the most remarkable part 

 of it is the existence of three stomachs. Teeth are never found 

 in these animals ; their aliments which are taken hold of by the 

 beak, are generally swallowed without being divided ; and do 

 not sojourn or pause in the mouth, as is the case in mammals ; 

 they have no veil of the palate (velum paJati,) to close this cavity 

 behind during mastication. {See, First Book of Natural History.) 

 The form of the beak varies much, and is always in relation to 

 the nature of the food made use of by the bird ; for this reason 

 it affords excellent marks or characters for the classification of 

 these animals. Sometimes the upper mandible is hooked and 

 fitted for tearing flesh, at others the beak is short, straight and 

 stout, suited to breaking grains ; at other times again it is wide 

 and very open, to enable the bird to seize easily in its flight, those 

 insects upon which it is destined to feed. 



27. The tongue is slightly fleshy, and covered with horny 

 papillae which serve to retain the food after it has entered the 

 mouth. The os hyoides (hyoid bone) which supports this organ, 

 is very much elongated, and terminates in two long delicate 

 horns which curve round the posterior and superior part of the 

 liead, their length depending on the extensibility of the tongue. 

 {Plate I, Jig. 3, and Plate 2,fg. 3.) 



23. The salivary glands are less numerous than in the mam- 

 malia ; all are placed beneath the tongue, and are formed of small 

 round grains, or granules. Generally the saliva is thick and 

 viscid. 



29. The oesophagus, ( Plate 2, fig. 4.) descends along the neck, 

 and generally presents, at its inferior part, a considerable dilata- 

 tion called the c/"o/? or /«c//?/fies; this pouch constitutes a first 

 stomach which projects above the clavicles ; it is very large in 

 granivorous birds and is met with in the Rapaces or birds of prey, 

 but is wanting in the Ostrich, and in most piscivorous birds, and 

 particularly those of the order of Grallatoriae. 



25. Are the organs of nutrition in birds the same as in mammals? 



26. In what particulars does the apparatus of digestion differ from that of 

 mimmals? 



27. What are the characters of the tongue in birds ? 



23. Have birds salivary glands ? What is the character of the saliva of birds ? 

 29. What is the crop or ingluties ? Is a crop found in all birds ? 



