136 



THE ELASMOBRANCH FISHES 



At the terminus of the pyloric division of the stomach is a circular band of 

 muscle fiber, the pyloric valve, separating the pyloric stomach from the duo- 

 denum or middle intestine. This valve varies considerably in extent in differ- 

 ent forms. In some types it shows only slight signs of constriction, as for ex- 

 ample in Heterodonfus, where it may allow food of considerable size to pass 

 into the spiral intestine. In Heptanchus we have seen that it projects as a well 

 defined circular band into the duodenum; and in Laemargus the valve is 

 greatly extended. 



In some of these forms an interesting condition obtains in which a room, the 

 bursa entiana, may be formed and into which the pylorus may empty. This 



A B C 



Fig. 135. Relation of the terminal part of the pylorus to the next segment, the duodenum. 

 A. Galeus. (From Eedeke.) B. Scym7ius. (From Helbing.) C. Hypnos. (Australian tor- 

 pedo.) (From Howes.) 



h.e., bursa entiana; d.ch., bile duct; prt., intraintestinal partition; p.v., pyloric, valve; 

 py., pylorus; spL, spleen; sp.v., spiral valve; y.s., yolk stalk. 



occurs in Galeus {h.e., fig. 135a) and in Cetorhinus. In Scymrius (fig. 135b) 

 such an enlargement is formed in a different way. Here the pylorus enters a 

 special room the upper part of which is the liursa entiana, and the lower is 

 continued into the intestine as a valve-free portion. In the Australian torpedo 

 Hypnos (fig. 135c) there is an interesting modification of this plan. The en- 

 larged room is separated into an anterior and a posterior chamber by an intra- 

 intestinal partition (pr^.). Into the former the pylorus (?jy.) empties and into 

 the latter the ductus choledochus (d.ch.) enters. 



Duodenum or Middle Intestine 



The duodenum may be encroached upon by the spiral valve through its entire 

 course, as in Heptanchus, or it may be free as in a few of the sharks and rays. 

 In a type like Spinax niger (fig. 136a) the valve-free portion is long. This 

 segment is present in Bhinohatis, but, of all the rays, it is best developed in 

 Trygon. In the great majority of types, however, the valve has so encroached 

 upon the pylorus that no free portion exists {Galeus, fig. 135a, Carcharias, 

 Lamnidae, Notidanidae, Scyllidae, Rhinidae, and some of the Rajidae). 



The proximal part of the duodenum shows different stages of complexity. 

 This may be illustrated by Spinax niger, where the pyloric tip is small and 



