. Bulletin. Natural history; Natuurlijke historie. BIOLOGY OF COSMINE 17. Fig. 3. Restorations of the arrangement of the pore-canal system in five Palaeozoic fishes, after Gross, 1956: A.) Poracanthodes, E) Tremataspis, C) Dipterus, D) Megalichthys, E) "Devonian ; ff = cross-canals; rf< = dentine tubules; m = Maschenkanal or upper mesh-canal; mc = mesh-canal; pc = pore-canal; pcv = pulp-cavity; pk = pulp-canal; po = pores; um =unter Maschenkanal or lower mesh-canal. Within the osteolepid rhipidistians one can therefore trace a process of reduction of the mesh-canal syst
. Bulletin. Natural history; Natuurlijke historie. BIOLOGY OF COSMINE 17. Fig. 3. Restorations of the arrangement of the pore-canal system in five Palaeozoic fishes, after Gross, 1956: A.) Poracanthodes, E) Tremataspis, C) Dipterus, D) Megalichthys, E) "Devonian ; ff = cross-canals; rf< = dentine tubules; m = Maschenkanal or upper mesh-canal; mc = mesh-canal; pc = pore-canal; pcv = pulp-cavity; pk = pulp-canal; po = pores; um =unter Maschenkanal or lower mesh-canal. Within the osteolepid rhipidistians one can therefore trace a process of reduction of the mesh-canal system to a single main channel and the formation of a prominent basal chamber in step with the reduction oi the unter Maschenkandlen. If one then compares the osteolepid fishes with osteostracan Agnatha such as Tremataspis (Gross, 1956, fig. 93) this process seems to be part of a consistent scheme of modification of the pore-canal system (see Fig. 3). In Tremataspis there is a completely double mesh-canal system with no basal chambers and only very small vertical pore-cavities. The two mesh-canals are separated only by a perforated septum. The arrangement of the pore-canal system in the holoptychoid rhipidistian Porolepis and in Devonian dipterid Dipnoi is comparable to that in Osteolepidae. Interestingly, in the earlier forms, there is a tendency for the whole pore-cavity system to be slightly deeper within the dermal skeleton and for a greater part of it to be enclosed within the spongiosa, than in 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 Peabody Museum of Natural History. New Haven : The Museum
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