Abstract
III.
IN the types already considered, the exo-skeleton consists of small placoid scales having the structure of teeth, and imbedded in the skin, but being altogether irrelative to the true cartilaginous endo-skeleton. In the group of fishes which form so perfect a mean between these Elamobranchs and the osseous fish-the Ganoids- the body is covered with close-set “ganoidv scales, which consist of two layers, a deeper one of bone (dermostosis), and a superficial one of enamel, covered only by a thin layer of epidermis. In the head these scales pass insensibly into a set of bones in close relation with the chondro-cranium, and having the connections, positions, & c. which characterise the roofing-bones of one of the higher skulls (parietais, frontals, nasals, & c). In many cases these bones are so deeply imbedded in the subcutaneous tissue as to deserve the name rather of par-ostoses than ofdermostoses, but are always easily removed by maceration or boiling. They are evidently of an entirely different nature to another series found in the same skulls, but in intimate connection with the cartilage, and only separable by its entire destruction. These last are ossifications of the chondro-cranium, and are often spoken of as “cartilage-bones;v the former kind have only a secondary relation to the primordial skull, and are known as i£ membrane-bones.”
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Report of Prof. Parker's Hunterian Lectures “On the Structure and Development of the Vertebrate Skull” * . Nature 10, 9–10 (1874). https://doi.org/10.1038/010009a0
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DOI: https://doi.org/10.1038/010009a0