356 RICHARD E. SCAMMON 



Its extent is but slight as compared with that of the posterior 

 portion of the gut, being at most not over 15 degrees. The 

 hinder and lower portion of the hepatic anlage is less affected by 

 this twisting than is the anterior free part presumably because its 

 attachment to the vitelline duct is still considerable in extent and 

 must offer some resistance to whatever force it may be that pro- 

 duces the rotation. That this portion of the alimentary tract 

 is affected to a slight degree however is shown by the broad 

 shallow groove which appears in the posterior half of the left wall 

 of the yolk-stalk and which has been figured and described in 

 the Normal plates (Scammon '11), under the term 'Lateral 

 groove of the vitelline duct,' and which may be seen in the figures 

 of reconstructions of embryos 7.5, 9 and 11.5 mm. in length 

 respectively, in that paper. The gut anterior to the yolk-stalk 

 also shows some rotation, being twisted to the right as is indicated 

 by the angle formed by its lumen with the mid-sagittal plane of 

 the body. 



PART II 



I. DESCRIPTION OF FULLY FORMED BILIARY APPARATUS 



Before attempting to describe the development of the gall 

 bladder and liver ducts, it may be well to outline the form of 

 these structures in the late embryo or new-born fish and to pre- 

 sent the terminology which will be employed in the remainder of 

 this paper. 



In large embryos and new-born specimens of Acanthias the 

 liver is a large viscus occupying nearly half of the abdominal 

 cavity. It consists of two lateral lobes which are united ante- 

 riorly by a median mass which stretches completely across the 

 body cavity posterior to the septum transversum. From the 

 right ventral and posterior margin of the median mass a small 

 pointed process extends backward and to the left. As the gall 

 bladder is imbedded in this mass it has been termed the cystic 

 lobe. The cystic lobe hes directly ventral to the stomach and 

 to the left of the cephalic end of the large internal yolk sac. 



