. Chordate morphology. Morphology (Animals); Chordata. 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 alon
. Chordate morphology. Morphology (Animals); Chordata. 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. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Jollie, Malcolm. New York, Reinhold
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