The relation of cartilage canals to the process of ossification
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1. A review of the literature on cartilage canals is given. 2. The formation of cartilage canals commences when the cartilage mass exceeds the maximum thickness which can be nourished by diffusion of fluid from the surface. This maximum thickness or the critical size at which canalization would occur, has been worked out in the distal femoral epiphysis at various developmental stages. It varies with the age of the foetus 0.25 mm. at the fourth month and gradually increasing to about 0.6 mm. at full-term. 3. Because of the restricted area of origin of the cartilaginous epiphysis of long bones, the canals seldom found, to be arranged in a radial fashion to the whole epiphysis, but they arranged so as to distribute the blood evenly through the whole mass. 4. (i) The clear, well-formed communicating canals have been seen in the epiphysis of human long bone as early as the fourth month of foetal life. (ii) As development proceeds, some of the communicating canals appear to become obliterated in, the region of proliferating cartilage adjacent to the metaphysis: this obliteration of canals occurs more rapidly after the onset of epiphyseal ossification so that by the time ossification of the epiphysis is complete, no communications between the diaphysis and the epiphysis remain. (iii) It is suggested that probably the primary cause of the formation of the communicating canal is the chemio-taxio influence in the zone of actively growing cartilage in the region adjacent to metaphysis, which directs the ends of the canals arising from the perichondrium near the end of the shaft to bend towards the diaphyseal end. (iii) The probable function of the communicating canals is that they assist in the supply of nutrition to and in the removal of waste products from the cells in the active juxta-metaphyseal cartilage. The almost invariable absence of osteogenic elements in these canals given no support to the hypothesis that they take part in the formation of the centre of epiphyseal ossification. (v) The vascular connective tissue buds which are identical with the communicating canals in the epiphysis of long bone, have boon observed in the cartilaginous sternal end of the clavicle of a human foetus. 5. It is suggested that the cartilage canals grow by a combination of three methods that is by surface accretion, stretching due to interstitial growth and active invasion of the cartilage by the tip of the canal. 6. The cartilage canal connective tissue contents are of perichondrial origin, and are not formed by back differentiation of the cartilage to an embryonic type of connective tissue. 7. In the long bone of the human, the cartilage canals are probably responsible for the formation of the epiphyseal ossification centre.
Thesis, PhD Doctor of Philosophy
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