124 THE ELASMOBRANCH FISHES 



SPLEEN 



The spleen (spl.) although unconnected with the digestive tract may be con- 

 sidered here. In Heptanchus this organ, when its relation to that in other 

 forms is studied, is very instructive. It consists of a long, more or less lobate 

 band extending from the ventral lobe of the pancreas over the greater (outer) 

 angle of the stomach. It then crosses over the stomach dorsally and is con- 

 tinued in the lesser curvature, one of its branches extending as far forward as 

 the tip of the cardiac portion {spl}, fig. 120) . 



Duodenum or Middle Intestine 



The part of the digestive tract immediately following the pylorus, the duo- 

 denum or middle intestine, is well defined in Heptanchus. In figure 120, this 

 segment {du.) is covered in part by the ventral lobe of the pancreas {pn}). 

 As in several other forms, the valve of the spiral intestine extends forward 

 throughout the length of the middle intestine and touches the pyloric valve. 

 Into this segment of the intestine the ducts of the liver and the pancreas empty. 



The liver {Iv., fig. 119) consists of a right and a left lobe between which is a 

 small caudate lobe, not shown in the figure. In the caudate lobe is located the 

 gall bladder which is emptied by a long duct (d.ch., fig. 120) into the duod- 

 enum. 



The entrance of the duct into the duodenum is of interest. It reaches and 

 enters the wall on the dorsal side only a short distance from the pyloric ter- 

 minus of the stomach. It then runs in the wall backward and outward on a line 

 almost at right angles to the attachment of the first whorl of the spiral valve. 

 After having encircled about one-fourth of the duodenal circumference it 

 empties into the duodenum a short distance from the first loop of the valvular 

 intestine. 



The pancreas is composed of two compact and connected lobes. The smaller 

 of these is dorsally placed {pn}, fig. 120), while the more compact lobe lies 

 ventrally on the angle between the pyloric division of the stomach and the 

 duodenum (pn.-) . The two lobes empty by a common duct which leaves the ven- 

 tral lobe and, passing through the duodenal wall, runs almost parallel with the 

 first annular artery. As it passes backward and outward it approaches the first 

 fold of the valvular intestine and finally empties into the duodenum only a 

 short distance to the left of (dorsally to) a line drawn from the entrance of 

 the bile duct at right angles to the first fold of the valvular intestine. 



Valvular Intestine 



The most interesting part of the intestine (figs. 120, sj^.i., and 123) is the spiral 

 valve contained within its cavity. The attachment of the valve to the intestine 

 may be seen from the outside as a series of annular folds traversed by blood 

 vessels, seventeen or eighteen turns of which are present in Heptanchus macu- 

 latus. By making a window in the vahailar intestine (fig. 123) it may be 



