774 



GENERATION AND DEVELOPMENT. 



uniform straight tube, which, gradually becomes divided 

 into its special parts, stomach, small intestine, and large 

 intestine (fig. 239). The stomach originally has the same 

 direction as the rest of the canal ; its cardiac extremity 

 being superior, its pylorus inferior. The changes of 

 position which the alimentary canal undergoes may be 

 readily gathered from the accompanying figures. 



A B Fly. 239.* C D 



The principal glands in connection with the intestinal 

 canal are the salivary, pancreas, and the liver. In Mam- 

 malia, each salivary gland first appears as a simple canal 

 with bud-like processes (fig. 240), lying in a gelatinous 

 nidus or blastema, and communicating with the cavity of 



* Fig. 239. Outlines of the form and position of the alimentary canal 

 in successive stages of its development (from Quain). A, alimentary 

 canal, &c., in an embryo of four weeks ; B, at six weeks ; C, at eight 

 weeks ; D, at ten weeks ; Z, the primitive lungs connected with the pharynx ; 

 s, the stomach ; d, duodenum ; i, the small intestine ; i', the large ; c, the 

 ccecum and vermiform appendage ; r, the rectum ; cl, in A, the cloaca ; 

 a, in B, the anus distinct from s i, the sinus uro-genitalis ; v, the yolk 

 sac ; v i, the vitello-intestinal duct ; u, the urinary bladder and urachus 

 leading to the allantois ; g, genital ducts. 



