OK THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 317 



G. The Liver and Biliary Apparatus. 



1. Superficial Anatomy (Figs. 4 and 13). 



The liver consists of two lobes — a large posterior and a smaller anterior. When the 

 body cavity is opened by a median ventral incision the anterior lobe is observed to 

 overlap the posterior, the latter on the left passing forwards under the anterior lobe. 

 On the right the gall bladder projects from a notch between, and dorsal to, the two lobes 

 of the liver, being partially overlapped by both, the right posterior extremity of the 

 one and the anterior extremity of the other being bevelled off to receive it. The 

 anterior border of the anterior lobe is just at the level of the two external branchial 

 openings. 



The sub-intestinal vein, formed by factors from the ventral wall of the anterior 

 abdominal gut, suddenly emerges from the gut wall opposite, or in front of, the posterior 

 end of the posterior lobe of the liver, and passes downwards along the hinder vertical 

 border of the hepatic ligament to reach the apex of the posterior lobe. From here it 

 passes forwards towards the sinus venosus along the entire length of the ventral surface 

 of the posterior lobe. A smaller branch, however, may be traced along the dorsal 

 surface. These conditions, or rather their superficial relations, vary in different 

 individuals. 



The mesentery, which suspends the gut, passes from the ventral wall of the gut on to 

 the posterior lobe of the liver as the hepatic ligament. It supports the posterior lobe 

 along its whole length, the only interruption being in the region of the gall bladder. 



The depression associated with the point of exit and entry of the posterior hepatic 

 duct and vessels is situated in the direct plane of the hepatic ligament. Hence the 

 two factors of the ligament, in passing straight on to the liver at this place, simply 

 diverge to allow the passage of the vessels. In front and on the right, the posterior 

 lobe of the liver is bevelled off dorsally to receive the gall bladder, whilst its anterior 

 extremity is overlapped ventrally by the anterior lobe. The two lobes are absolutely 

 distinct, each having its own independent serosa.* 



In the region of the gall bladder the mesentery passes loosely from the gut on to 

 the right side of the gall bladder. This admits the passage of the various ducts and 

 vessels associated with the gall bladder and the two lobes of the liver. From the left 

 side of the gall bladder the mesentery is reflected on to the dorsal surface of that portion 

 of the posterior lobe of the liver in front of the depression mentioned above. 



Unlike the posterior lobe, the anterior lobe of the liver has no definite ligament, but 

 its posterior edge usually more or less adheres to the posterior lobe. The mesentery 

 passes on to it from the anterior left surface of the gall bladder, and reaches it immedi- 



* This statement must be qualified. In one series of sections I found a slight but quite unmistakable fusion of 

 the glandular tissue of the mesial edge of the posterior lobe and the dorsal surface of the anterior lobe in the region 

 of the overlap a little to the left of the middle line of the body. Further, in one dissection the two lobes of the liver 

 were completely fused into one body. 



TRANS. ROY. SOC. EDIN., VOL. XLIX. PART II. (NO. 3). 41 



