868 



DEVELOPMENT 



[CH. LIX. 



remains as a diverticulimi from the intestine, Meckol's diverticulum. 

 Sometimes a fibrous cord, attaching some part of the intestine to the 

 umbilicus, remains to represent the vitelline duct. Such a cord has 

 been known to cause, in after-life, strangulation of the bowel and 

 death. 



The -alimentary canal lies in the form of a straight tube close 

 beneath the vertebral column, but it gradually becomes long, con- 



FIG. 666. Outlines of the form and position of the alimentary canal in successive stages of its develop- 

 ment. A, Alimentary canal, etc., in an embryo of four weeks ; 13, at six weeks ; C, at eight weeks* 

 I, the primitive lungs connected with the pharynx ; s, the stomach ; d, duodenum ; i, the small 

 intestine ; i', the large intestine ; c, the caecum and vermiform appendage ; r, the rectum ; d, in 

 A, the cloaca ; a, in B, the anus distinct from si, the sinus uro-genitalis ; v, the yolk-sac , vi, the 

 vitello-intestinal duct ; u, the urinary bladder and urachus leading to the allantois ; g, genital 

 ducts. (Allen Thomson.) 



voluted, and divided into its special parts, stomach, small intestine, 

 and large intestine (fig. 666), and at the same time comes to be 

 suspended in the abdominal cavity by means of a lengthening 

 mesentery formed from the splanchnopleur which attaches it to the 

 vertebral column. The stomach originally has the same direction as 

 the rest of the canal ; its cardiac extremity being superior, its pylorus 

 inferior. These changes of position may be readily understood from 

 the accompanying figures (fig. 666). 



Pancreas and Salivary Glands. The principal glands in con- 

 nection with the intestinal canal are the salivary glands, pancreas, 

 and the liver. In mammalia, each salivary gland first appears as 

 a simple canal with bud-like processes, lying in a mass of mesoblast, 

 and communicating with the cavity of the mouth. As the develop- 

 ment of the gland advances, the canal becomes more and more 

 ramified (fig. 667). The submaxillary and sublingual glands and 



