380 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



glandular walls ; then comes the gizzard, composed of two thick, red, 

 striped muscles, covered internally with a thick, horny epithelium. 

 The gastric parts of this class of birds are therefore divided into three 

 sections — first, the crop, to act as a reservoir, in which the food is macer- 

 ated ; from this it is pushed gradually into the second, the stomach, in 



which it undergoes gastric 

 digestion simultaneously 

 with the process of tritura- 

 tion which occurs in the giz- 

 zard, or the third digestive 

 compartment (Fig- 154). 

 Grains, etc., which form the 

 food of gallinaceous birds, 

 first go into the crop, which 

 thej' distend, and in which 

 they accumulate in consid- 

 erable quantity. Here the 

 food becomes softened and 

 takes on an acid reaction. 

 A comparatively profuse se- 

 cretion is poured out in this 

 pouch, whose properties 

 have not been thoroughly' 

 investigated. B} T inserting 

 substances into the crop, 

 Spallanzani obtained one 

 ounce of fluid in twelve 

 hours from the crop of a 

 pigeon, and seven ounces of 

 the fluid from a guinea-hen ; 

 but although this fluid is 

 thus poured out in consid- 

 erable amount, it does not 

 appear to be very active in 

 softening the food. It is 

 not known that this secre- 

 tion has any digestive prop- 

 erties, although it seems 

 probable that starch would 

 here be converted into sugar, since grain remains in this compartment for 

 twelve or thirteen hours, or even much longer. After leaving the crop, 

 the food then passes into the veutriculus and gizzard. The ventriculus is 

 supplied with a large number of tubular glands, which secrete an acid fluid. 



Fig. 154,— Crop and Stomach of the Pigeon. 

 (Bernard.) 



MM, crop; I, (esophagus ; C, provontriculus : S. tubular glands of 

 stomach; J, gizzard ; D, duodenum. 



