THE ELASMOBRANCH FISHES 



139 



mesentery into the lesser angle. In other words, in addition to the type of 

 spleen on the onter angle characteristic of sharks, Heptanchus also has splenic 

 tissue on the inner angle of the stomach like that of the rays. 



Valvular Intestine 



The valvular intestine receives its name from the fact that it contains within 

 its lumen a membranous fold or valve. This fold as a general thing in the 



A B C 



Fig. 138. Valvular intestine. (From T. J. Parker.) A. Attachment in Zijgaena. B. Valve in 

 Scyllium. C. Valve in Zygaena. 



Elasmobranchs is spiral in nature, and produces a spiral valve. In a few forms, 

 however {Zijgaena), it is of the scroll type, with the line of attachment along 

 the wall of the intestine only slightly curved (fig. 138a). This valve in Zy- 

 gaena (fig. 138c) is rolled up within the intestine and has a width two-thirds 

 of its length. 



Seen from the outside the spiral valve presents the aspect of a screw over 

 the threads of which has been wrapped some thin substance through which the 

 threads are evident superficially. But such a likeness would be correct only if 

 the threads grew from and were a part of the outer covering. 



