. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Division of Labor in Tissues 151 acquire the ability to produce cartilage or bone. Although at first all of the bony tissue is of the spongy type, a thick region on each surface is later con- verted into compact bone, leaving inside a filler of spongy tissue in which the spaces are occupied by bone marrow. The connective tissue membrane which remains as a covering of the bones is called the periosteum. In the case of a replacing bone like the tibia of the
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Division of Labor in Tissues 151 acquire the ability to produce cartilage or bone. Although at first all of the bony tissue is of the spongy type, a thick region on each surface is later con- verted into compact bone, leaving inside a filler of spongy tissue in which the spaces are occupied by bone marrow. The connective tissue membrane which remains as a covering of the bones is called the periosteum. In the case of a replacing bone like the tibia of the lower leg (shank), a cartilaginous rod is laid down in the connective tissue. Later this cartilage is replaced by bone in somewhat the following manner. Some of the peri- chondrial cells and others in- side of the cartilage near the middle of the rod become bone builders (osteoblasts) and lay down a ring of bone at that point. Adjacent to this ring the cartilaginous matrix begins to dis- solve, probably under the influ- ence of certain cells which have been called chondroclasts. As fast as the cartilage is destroyed, spongy bone takes its place (Fig. 107). From the middle of the bar these changes spread toward the ends until the entire shaft (dia- physis) has ossified leaving only the ends (epiphyses) of the tibia as cartilage. This is the condition in man at about the time of birth. Soon after birth a center of ossi- fication appears in each epiphysis and enlarges until the only cartilage left here is a cap on the articular surface and a plate between diaphysis and epiphysis (Fig. 108). The articular caps remain throughout life but the plate is a temporary device to permit elongation of the bone. The cartilage in the middle of the plate continues to grow and expand. At the same time the process of minute replacement goes on at the two surfaces where it is in contact with diaphysis and epiphysis. At an age of 17-25 years the cartilage of the plate ceases regeneration and the in
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Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
