bile duct. 



pylorus 



— pharynx - 



-Stomach esophagus- 



dorsal diverticulum , 



folds of stomach lining 



pyloric valve 

 bursa en 



LAEMARGUS BOREALIS 



pylorus 



spiral valve 



spleen 

 B SCYMUS LICHIA 



spleen 



C MUSTELUS LAEVUS 



Figure 9-21 . Pyloric caeca in toemargus borealis, A, and Scymus lichia, B, and internal view of 

 stomach and anterior end of gut of Mustelui /oevus, C. (After Pernkopf and Lehner, 1937) 



end of the midgut. The pancreas is a band-like mass lying 

 along the hepatic portal channel, which drains the spleen 

 and the wall of the gut. The intestinal vein from the spiral 

 valve and anterior gut wall enters the hepatic portal stem 

 at the anterior end of the pancreas. The pancreatic duct 

 passes forward along this channel to enter the bile duct. The 

 spleen is a triangular body lying above the gut and is at- 

 tached to the pancreas anteriorly, with its tapered end di- 

 rected posteriorly. 



The holocephalan agrees with the shark in lacking a sep- 

 arate midgut and in having a compact pancreas. The lack 

 of a distinct stomach has been considered primitive, but 

 could as easily be the result of loss (a specialization). The 

 development of the holocephalan is assumed to be like that 

 of the shark but has not been fully studied. 



General observations on gnathostome fishes 



The intestines of the chondrichthyes, choanates, and Pofy- 

 pterus agree in lacking a distinct midgut — the spiral or rolled 

 valve extends through almost the entire length of the in- 

 testine. Bothriolepis, an antiarch, is described as having a 

 similar intestine with a rolled valve. The primitive members 

 of the actinopterygian groups have a spiral valve in the 



rectal gland 



Figure 9-22. Rolled valve of intestine of Zygaena. A, ventral wall of 

 gut removed to show the valve; B, cross section of gut and valve. 



274 • THE VISCERA 



