. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. The Structure of Dinichthys 157 factory curvirtg of this part, so as to fit the head roof together with the side plates, we must admit that the plates in the front region are not only crushed, cleft and slid, but flattened and deformed by pressure. We may call this kind of deformation microstructural. The plate in such a case is apparently not destroyed; it shows no clefts or breaks. But under enormous pressure it was flattened and became thinner and larger. This deforma' tion can be perceived only by study o
. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. The Structure of Dinichthys 157 factory curvirtg of this part, so as to fit the head roof together with the side plates, we must admit that the plates in the front region are not only crushed, cleft and slid, but flattened and deformed by pressure. We may call this kind of deformation microstructural. The plate in such a case is apparently not destroyed; it shows no clefts or breaks. But under enormous pressure it was flattened and became thinner and larger. This deforma' tion can be perceived only by study of sections under the microscope. The whole bone becomes more or less laminated in character. The Haversian canals, placed parallel with the surface of the plate, are flattened; those placed obliquely or perpendicularly to it are enlarged. All the bone-cell cavities are also flattened. Good pictures of such a microstructurally deformed bone are to be found in Heintz, (PI. XXII, fig. 3; PI. XXIV, fig. 4). In reconstructing the curve of the front part of the head roof, the position of SO is of aid. As we have seen, on the front part of the handle of SO there were some ridges, which served to attach SO to the pre-orbital process of the head roof. On the latter were also developed some sockets and ridges. Text'figure 39 shows the fore part of SO and the pre-orbital process. It demonstrates how well the single processes and sockets were adapted to one another and how intimately these two parts were connected. But if the handle of SO is attached to the PrO of a compressed specimen, the hind part of it, the blade, stands far out from the side margin of the head roof (Text-figure 40). Mean- while, we know that the upper fore cor- ner of the blade should touch a notch behind the post-orbital process and the edge of the blade should run along the side margin of the head roof. To attain such a position of SO, it is not enough to curve the handle, the front part of the head also must
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