INTESTINE. 129 



valve, close to whicli the ductus choledochus enters, indicating 



Fig. 55. — Siphonal stomact and spiral valve of Basking-Shark (Selache). 

 (After Home and Owen.) 

 a, (Esophagus ; h, Cardiac portion of stomach ; c, pyloric portion ; d, pouch in- 

 termediate between stomach and duodenum, with circular valves at both 

 ends ; e, Duodenum ; /, Valve of intestine ; g. Ductus hepaticus ; li, Spleen. 



the boundary of the intestine proper (Fig. 57, f). The spiral 

 valve is perfect, and makes from three {Chimoira) to nine 

 (Ceratodus) gyrations. A cloaca is present, as in Chon- 

 dropterygians. A mesentery fixing the dorsal side of the 

 intestine is absent. 



The other Ganoids resemble again more the Chondrop- 

 terygians in the structure of their intestinal tract. The 

 stomach has always a distinct pyloric portion, and has a still 

 more complicated structure in Acipenser. The duodenal 

 portion receives the contents of Appendices pyloricm, which 

 are confluent into a gland-like mass in Acipenser, but separate 

 in Polyodon, and numerous and short in Lepidosteus, whilst 

 Polypterus possesses one such appendage only. A spiral 

 valve is developed in the Sturgeons and Polypterus, but in 

 Amia, in which the intestine performs several convolutions, 



K 



