48 THE STRUCTURE OF THE FOWL 



partly separated from each other by consider- 

 able clefts (Fig. 19). The common cavity into 

 which the cluster, or lobule, of glands opens is 

 lined by columnar cells, and has a relatively 

 narrow duct— the walls of which are folded — 

 opening on the surface of the mucous membrane. 

 2. The muscular stomach, or gizzard (Figs. 

 12, 15, and 22), immediately succeeds the 

 glandular stomach, from which it is separated 

 merely by a constriction. Placed partly between 

 the two lobes of the liver and partly behind 

 the left lobe, the gizzard is flattened and 

 rounded somewhat like a bi- convex lens — 

 one diameter, however, slightly exceeding the 

 other. Each surface is covered by a glistening 

 tendinous layer, thicker at the centre of the 

 surface and thinning away towards the margins. 

 A section of the organ along its greatest, or 

 antero-posterior, diameter shows that the centre 

 of each surface contains no muscle (Fig. 20) ; 

 while the cranial and caudal extremities are 

 formed by two powerful masses of red muscular 

 tissue, united by a much thinner stratum along 

 the borders of the gizzard. The interior is 

 furnished with a pale, thick, and horny lining, 

 raised into ridges ; and almost always contains 

 hard substances, such as small pebbles, etc., 



