. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. 130 Bashford De^n Memorial .Volume little rough and often shows the ossification centres and the ossification rays. Very seldom can there be found a fine tuberculation in the region ot the ossification center, The present writer has seen this phenomenon only twice. Moreover, the outside of the head also shows quite deep grooves for the sensory canals and the limits between the single plates. The latter are, however, often very obscure. ' The whole head roof was in reality strongly curved from side to side and
. The Bashford Dean memorial volume : archaic fishes. Fishes; Sharks; Fishes, Fossil. 130 Bashford De^n Memorial .Volume little rough and often shows the ossification centres and the ossification rays. Very seldom can there be found a fine tuberculation in the region ot the ossification center, The present writer has seen this phenomenon only twice. Moreover, the outside of the head also shows quite deep grooves for the sensory canals and the limits between the single plates. The latter are, however, often very obscure. ' The whole head roof was in reality strongly curved from side to side and from back to front. But during the fossilization process it was more or less flattened, crushed and broken. Later we shall come back to this matter and see how we can reconstruct the real curving of the head roof. The inside of the head roof shows a much more intricate picture (Text-figures 13 and 14, and Plate II). The hinder margin is strongly thickened. From both the joint processes (Jp), massive thickenings run along the margins, meeting one another in the median line at an angle of about 110° and connected, just before they run together, by a thick transverse commissure (tc). The triangular place between this commissure and the above mentioned thickenings is occupied by a very deep double socket (ds). The curved part of the hind mar- gin in front of the commissure is thin {mp). The structure of the joint sockets will be described in detail in a later section. From the point of union the single thickening continues upward along the median line to about one-third of the whole length of the head roof. Here it suddenly stops and forms a transverse sharp limit (tri). The whole of this massive part of the shield composes the posterior consolidated arch (PCA) of the head roof. The two other consolidated parts are placed symmetrically along the side margin of the head roof (LCP). They begin at the front of the head roof and at first are about one'third of its breadth, but in the
Size: 1360px × 1837px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., book, bookcentury1900, booksubjectfishes, booksubjectfishesfossil
