. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 322 AVES. Pigeons, however, are known to carry gravel to their young. Gallinaceous birds grow lean if deprived of pebbles; and no wonder, since experiment* shows that unless the grains of corn are bruised, and deprived of their vitality, the gastric juice will not act upon or dissolve them. The observations and experiments of Hunter have completely established the rationa- lity and truth of Redi's opinion, that the peb- bles perform the vicarious office of teeth. Hunter inferred from the form of hair-balls occasionally f
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 322 AVES. Pigeons, however, are known to carry gravel to their young. Gallinaceous birds grow lean if deprived of pebbles; and no wonder, since experiment* shows that unless the grains of corn are bruised, and deprived of their vitality, the gastric juice will not act upon or dissolve them. The observations and experiments of Hunter have completely established the rationa- lity and truth of Redi's opinion, that the peb- bles perform the vicarious office of teeth. Hunter inferred from the form of hair-balls occasionally found in the stomach of Cuckoos,+ that the action of the great lateral muscles of the gizzard was rotatory. Harvey appears to have first investigated, by means of the ear, as it were in anticipation of the art of auscultation, the actions which are going on in the interior of an animal body, in reference to the motions of the gizzard. He observes, (De Gencratione Animalium, hi Opera Omnia, 4to. p. 208,) " Fal- conibus, aquilis, aliisque avibus ex preda viven- tibus, si aurem prope admoveris dum ventricu- lus jejunus est, manifestos intus strepitus, lapillorum illuc ingestorum, invicemque colli- sorum ; And Hunter observes, (Animal (Economy, p. 198,) " the extent of motion in grindstones need not be the tenth of an inch, if their motion is alternate and in con- trary directions. But although the motion of the gizzard is hardly visible, yet we may be made very sensible of its action by putting the ear to the sides of a fowl while it is grinding its food, when the stones can be heard moving upon one ; Tiedemann believes that the muscles of the gizzard are in some degree voluntary, having observed that when he placed his hand oppo- site the gizzard, its motions suddenly stopped. The pyloric orifice of the gizzard is guarded by a valve in many birds, especially in those which swallow the largest stones. This valve in the Ostrich is formed by a r
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