180 THE DEVELOPMENT OF THE CHICK 



of the anterior intestinal portal becomes incorporated in the 

 floor of the intestine as the anterior intestinal portal retreats 

 backwards, and the original dorsal liver diverticulum therefore 

 becomes anterior or cephalic and the ventral becomes posterior 

 or caudal (Fig. 103 B). Before this transposition occurs, how- 

 ever, the diverticula have grown forward towards the sinus 

 venosus in the ventral mesentery of the stomach, the anterior 

 diverticulum above and the posterior diverticulum below the 

 ductus venosus. The stretch of entoderm between the two liver 

 diverticula thus lies in the angle made by the union of the two 

 omphalomesenteric veins. At the stage of 26 somites, the anterior 

 diverticulum has grown forward above the ductus venosus 

 to the level of the Cuvierian veins and is large and flattened 

 laterally. The posterior diverticulum is barely indicated at this 

 time. 



The anterior diverticulum was originally described as left and the 

 posterior as right (Goette, 1867), and this description was taken up 

 by Foster and Balfour. This was corrected by Felix (1892). Subse- 

 quent writers do not agree exactly as to the time or precise relations 

 of the diverticula; however, it is generally agreed that the two diver- 

 ticula are subdivisions of a common hepatic furrow, inasmuch as the 

 entoderm between them lies below the level of the entoderm in front 

 and behind (Fig. 103 B). Brouha maintains that at first the hepatic 

 furrow lies in front of the anterior intestinal portal, and that the latter 

 secondarily moves forward so as to include the hepatic furrow, which 

 later again comes into the floor of the intestine with the definitive retreat 

 of the anterior intestinal portal. This view does not rest on very secure 

 evidence, and is probably based on interpretation of slight individual 

 variations as successive stages of development. Choronschitzky places the 

 time of appearance of the hepatic diverticula at about the thirty-sixth 

 hour. It is probable, however, that this is too early. I have found the 

 first unmistakable diverticulum at a stage of 22 somites, a slight rudi- 

 ment of the anterior diverticulum in the anterior intestinal portal. 



At the 30 s stage the anterior or dorsal diverticulum has ex- 

 panded much more, mainly to the left of the middle line, as though 

 to embrace the ductus venosus, and the posterior or ventral 

 diverticulum has an even greater development and embraces 

 the right side of the ductus venosus, but it does not extend as 

 far forward as the anterior diverticulum. Both diverticula 

 now branch rapidly and profusely, forming secondary anasto- 



