. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. SKELETON. 43 and those passing through a cartilage stage (cartilage bones) can only be recognized by following the ontogeny of the element in question. As stated above, there is much evidence to show that the membrane bones are dermal bones which have sunk to a deeper position and have become secondarily associated with the endoskeleton. This is especially evident in the skulls of some of the lower ganoids. Ossification of cartilage takes place in two ways. In ectochondrostosis the deposit of lime salts begins

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. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. SKELETON. 43 and those passing through a cartilage stage (cartilage bones) can only be recognized by following the ontogeny of the element in question. As stated above, there is much evidence to show that the membrane bones are dermal bones which have sunk to a deeper position and have become secondarily associated with the endoskeleton. This is especially evident in the skulls of some of the lower ganoids. Ossification of cartilage takes place in two ways. In ectochondrostosis the deposit of lime salts begins
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Image ID: REFED6
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. SKELETON. 43 and those passing through a cartilage stage (cartilage bones) can only be recognized by following the ontogeny of the element in question. As stated above, there is much evidence to show that the membrane bones are dermal bones which have sunk to a deeper position and have become secondarily associated with the endoskeleton. This is especially evident in the skulls of some of the lower ganoids. Ossification of cartilage takes place in two ways. In ectochondrostosis the deposit of lime salts begins on the deeper surface of the perichondrium and gradually invades the cartilage. In entochondrostosis the cartilage becomes broken down in the interior, some of the cells becoming modified into osteoblasts, and from these as centres of ossification, the process of bone forma- tion extends in all directions. In ectochondrostosis at least, the centres of ossifica- tion may have been derived, phylogenetically, from elements of the dermal skeleton. In ossification the bone is developed in layers, between which the osteoblasts are arranged. In the elasmobranchs the skeleton is frequently strengthened by deposits of lime, but this calcified cartilage differs from bone in that the deposits of lime take the form of polygonal plates and there are no lacunae.. FIG. 36.—Diagram of growth of bone. A, from an animal recently fed with madder causing a layer of bone (black) colored by the dye; B, later, no madder fed for some time, a deposit of colorless bone on outside of colored layer, internal layer thinner; C, still later, outer layer thicker, inner layer absorbed. Many bones increase in length by the addition of epiphyses at the ends. These are separate ossifications which only unite with the main bone at the time the adult condition is reached. The increase in diameter has some interesting features. In animals fed with madder, the bone formed during the feeding is colored. In this way

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