. Elements of Comparative Anatomy. 28 COMPARATIYE Fig. 11. Eana. o bone-cells found in the skeletal organs of all classes of tlie Vertebrata; whilst that form of osseous tissue witli canaliculi only is found in the skeleton of many fishes, and as a general rule in the dental organs of all Vertebrata (dentine). The development of osseous tissue explains the relations of the intercellular substance to the cells. That form of it which contains cells may arise in two ways: either by the ossification of con- nective tissue, the cells in which become converted into bone-cells by the ossi-
. Elements of Comparative Anatomy. 28 COMPARATIYE Fig. 11. Eana. o bone-cells found in the skeletal organs of all classes of tlie Vertebrata; whilst that form of osseous tissue witli canaliculi only is found in the skeleton of many fishes, and as a general rule in the dental organs of all Vertebrata (dentine). The development of osseous tissue explains the relations of the intercellular substance to the cells. That form of it which contains cells may arise in two ways: either by the ossification of con- nective tissue, the cells in which become converted into bone-cells by the ossi- fication of the intercellular substance, which becomes impregnated with calca- reous salts, while the cells themselves become con- nected with one another by their processes, which traverse the pore-canals ia the intercellular substance; or the same tissue is formed by apparently indifferent cells, which secrete a scle- rogenous substance. This substance is laid down in stratified lamellae, into which the secreting cells send fine protoplasmic processes (Fig. 11, o). The secretion of this substance is preceded by a change of part of the protoplasm of the cell. As soon as this is differentiated it does not belong any longer to the cell, and is therefore secreted from it. If some of the secreting cells (o'o") cease to be active, while the cells near them do not cease to be so, the former gradually get to lie in a layer of intercellular substance, which finally surrounds them, and so converts them into bone-cells (o'"). The cells of the secreting layer (osteoblasts) are continuously connected by fine processes with those which are already enclosed (bone-cells). Thus each of the former is rendered capable of becoming a bone-cell. The other form of osseous tissue is developed in a perfectly analogous manner, so far as its history is accurately known, through the development of dentine. In this case also a layer of cells secretes a substance, which hardens or is sclerogenou
Size: 1628px × 1536px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookcentury1800, bookdecade1870, bookpublisherlondonmacmillan
