ALIMENTARY TRACT AND ITS APPENDAGES 313 



in front of and behind it (Fig. 150). No detailed account of its 

 development exists. 



Stomach. It is well known that the stomach of birds exhibits 

 two successive divisions, the proventriculus and the gizzard, 

 the former of which has a digestive function and is richly pro- 

 vided with glands, while the latter has a purely mechanical func- 

 tion, being provided with thick muscular walls, within which is 

 the compressed cavity lined on each side by tendinous plates. 



On the third day of incubation, the divisions of the stomach 

 are not recognizable, either by the form of the entire organ or by 

 the structure of the walls. On the fifth day, however, the first 

 indications of the formation of the compound glands of the 

 proventriculus may be seen in the cardiac end; the posterior or 

 pyloric end occupies the extreme left of the gastric curve and 

 forms the rudiment of a blind pouch projecting posteriorly, that 

 develops into the gizzard. On the sixth and seventh days this 

 pouch expands farther in the same direction (cf. Fig. 179), and a 

 constriction forms between the anterior portion of the stomach, 

 or proventriculus, and the gizzard, as thus marked out. The 

 gizzard grows out farther, to the left and posteriorly, at the same 

 time undergoing a dorso-ventral flattening, owing to the forma- 

 tion of the large muscle-masses. According to this account, 

 therefore, the greater curvature of the gizzard would represent 

 the original left side of the portion of the embryonic stomach 

 from which it is derived, and the original right side would be 

 represented by the lesser curvature. 



The large compound glands of the proventriculus are indi- 

 cated on the fifth or sixth days as slight depressions of the ento- 

 derm towards the mesenchyme; on the seventh day these become 

 converted into saccular glands with narrow necks (Fig. 182). 

 Each sacculus becomes multilobed about the twelfth or thirteenth 

 days, and each lobulus includes a small number of culs-de-sac, 

 lined with a simple epithelium. The last subsequently become 

 tubular, and the original sacculus then represents the common 

 duct of a large compound gland. (See Cazin.) 



The simple, tubular glands of the gizzard begin to form about 

 the thirteenth or fourteenth day, and the lining of the gizzard 

 is simply the hardened secretion of these glands; it is thus essen- 

 tially different from cuticular and corneous structures of the sur- 

 face of the body. According to Cazin, the glands of the gizzard 



