242 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



to this the end of the roof is marked by a backwardly directed 

 fringe. The large tongue attached to the floor of the mouth, 

 has a sharply-pointed tip directed forwards, and its hinder part 

 is produced backwards into fringed processes, behind which is 

 the glottis, a narrow slit, with edges also somewhat fringed. The 

 back part of the mouth-cavity, or pharynx, is continued behind 

 into a very long gullet (oesophagus), for the most part with thin 

 walls, which runs back on the ventral side of the neck to reach 

 the thorax. In the posterior part of the neck it dilates into 

 the crop, a very large bilobed sac, with extensible walls. Behind 

 this the gullet narrows, and its walls are much thicker. It 

 passes in the thorax into a small oval chamber, the proventri- 

 culus, of somewhat larger calibre, and with thick soft walls, 

 upon the inner surface of which are a number of small rounded 

 apertures, those of the peptic glands. The proventriculus opens, 

 on the left side, into the dorsal border of the gizzard, a large 

 rounded, somewhat flattened structure with extremely thick 

 hard walls, the lining of which is horny. It contains numerous 

 small pebbles and other foreign bodies which have been 

 swallowed. Proventriculus and gizzard together are equivalent 

 to a stomach. A narrow tube, the small intestine, comes off 

 from the right side of its dorsal border, forms a U-shaped loop, 

 the duodenum, and, after making several loops and coils, merges 

 into the short, straight, large intestine, the junction between the 

 two being marked by a pair of small projections, the intestinal 

 cceca. These are very large in the fowl. The large intestine is 

 continued posteriorly into a small cloaca which opens externally 

 by the cloacal aperture. The cloaca is divided by inwardly pro- 

 jecting folds into three compartments, internal, middle, and 

 external (Fig. 71). The first receives the large intestine, the 

 second the urinary and genital ducts, while into the dorsal wall of 

 the third a small thick-walled pouch, the bursa Fabricii, opens in 

 young birds. The lining of the small intestine is raised into 

 innumerable delicate thread-like processes, the mlli, which gradu- 

 ally die away posteriorly and are replaced by longitudinal ridges. 



The lining of the large intestine and cloaca is smooth. 



The liver is a large, brown organ, lying on the ventral side of 

 the body, and presenting depressions above and in front into 

 which the heart, duodenum, and gizzard fit. It is divided into 

 right and left lobes, of which the first is the larger. There are 



