76 GRIFFIN. 



beneath the muscular wall, and finally open into the pharyngeal 

 cavity near the anterior ends of the lateral lamellae, as previ- 

 ously mentioned (page 74) . 



The oesophagus is a straight tube about 25 millimeters in 

 length. Its mucous membrane is thrown into numerous^ 

 straight, longitudinal folds. The oesophagus opens into a thin- 

 walled saccular crop, about 12 millimeters long by 15 millimeters 

 in diameter. The opening of the oesophagus into the crop is 

 guarded by a strong sphincter muscle and, also, by an annular 

 fold of the mucous membrane of the oesophagus, which pro- 

 jects backward into the crop (fig. 13, Plate III). The mucous 

 membrane of the crop is smooth. 



The crop is followed by a muscular, barrel-shaped gizzard, 12 

 millimeters long by 17 millimeters in diameter. The muscular 

 wall of the gizzard consists of a thick, complete ring of circular 

 muscles, thickest at the center and thinning regularly toward 

 each end. The interior of the gizzard is almost completely 

 filled by roughly pyramidal, chitinous "stomach-plates," usually 

 about 10 in number, which occupy the greater part of the wall. 

 A row of from 9 to 11 small plates stands in front of these. 

 The plates have about the same consistency as fresh hyaline 

 cartilage, and are of a light coffee-color. The food of the animal 

 consists of the animal and plant substances which are mixed 

 with the bottom sand, which must be very effectively ground in 

 passing through the narrow passages between these plates. It 

 appears probable that the trituration of the food is accomplished 

 more by the sand grains which are mixed with it than by the 

 direct action of the stomach plates. The arrangement of 

 the latter is such as to leave only tortuous, narrow passages 

 through the gizzard when that organ is relaxed. When its 

 muscular walls contract, the sand grains contained in the pas- 

 sages will be pressed against each other and against any food 

 substances present, producing a comminuting action much more 

 effective than can be attained by the direct action of the large, 

 blunt, and somewhat soft plates. The large stomach plates are 

 bluntly pointed, with the points directed slightly backward. 

 Each plate presents 3 or 4 prominent, somewhat irregular, but 

 not sharp edges (figs. 17 and 18, Plate III). The bases of the 

 plates are slightly convex and, in general, ovoid in outline. The 

 center of the plate is occupied by an axial column of darker 

 color and slightly harder material than the outer part, which is 

 exposed upon the worn tip of the plate. 



The plates are composed of numerous, thin layers, parallel to 



