DEVELOPMENT OF THE ELASMOBRANCH LIVER 375 



24 of an embryo 60 mm. in length shows a specimen in which the 

 rotation of the ductus choledochus to the right must have been 

 very great indeed for it still shows an almost right angled curve 

 in that direction at this late stage and the right medial, the left 

 medial, and the anterior left rami all arise from it between the 

 ostia of the cystic and left hepatic and the right hepatic duct. 

 The figure of an embryo of 86 mm. (fig. 25) shows the most 

 extreme case of the series in which both the left and the right 

 anterior rami arise from the right hepatic duct, the latter almost at 

 its ostium. I can only explain this case on the supposition that 

 the posteriorly directed proximal segment of each the right and 

 left main hepatic ducts is derived in part by a splitting off from 

 the ductus choledochus and that the left medial ramus originally 

 connected with an area of the right side of the ductus choledochus 

 which was later incorporated in the distal end of the right lateral 

 hepatic duct. 



That other variations in the arrangement of these hepatic rami 

 may occur both in embryo and adult is very probable, but it is 

 to be expected that they will all be of the same general type as 

 those described above, viz., such as may be brought about by the 

 progression of their ostia from left to right. Besides the variation 

 in position of ostia, there are also noticeable ones in the size of the 

 various elements. This seems to be compensatory in that the re- 

 duction in extent of any element is accompanied by an increase in 

 size and complexity of its neighbors. Occasionally one element 

 may be replaced by two or more smaller ones and minor rami are 

 commonly found irregularly -placed in regard to the larger ones. 

 These minor sprouts as already stated arise either from tubules 

 intermediate in position to the main tubule groups or from such 

 tubules as arise after these groups are somewhat separated from 

 the main ducts by pedicles. A scheme of the origin of the minor 

 ducts or rami will be found in the general summary in table 3. 



