ISSN:
1573-6865
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Conclusions Evidently it is the circumstances of tissue association which are important with regard to the differentiation of NC-derived cells into primary cartilage and membrane bone. Tissue interactions of this sort apparently do not play a role in the differentiation of secondary cartilage, where simply theposition of NC-derived cells and their progeny within the early membrane bone primordium determines whether or not those cells will subsequently express a secondary chondrogenic potential. Whether we are considering the type of tissue association generated or the ‘specification’ of cell positioning, both are controlled by the parameter of NC cell migration. Thus disturbances in the conditions of migration, for instance retarded migration or incorrect timing, will generate anomalies of cranio-facial morphogenesis and of skull development, (Johnstonet al., 1977; Morriss & Thorogood, 1978). Furthermore, as phylogenetic differences in (skull) form are generated by changes in developmental mechanisms, simple quantitative changes in such parameters as NC migration and proliferation will have profound evolutionary consequences (see, for example, Kollar & Fisher, 1980). This review started by asking the question ‘How, in a developmental sense, does one build a skull?’ That question has not been answered but a few suggestions have been provided as to the rules of the developmental programme whereby the various skeletal tissues are laid down in a skull-specific pattern. It seems that these rules can be defined in terms of timing, circumstances of tissue association and spatial positioning of cells. A comprehensive identification and fuller recognition of rules such as these is, I propose, a pre-requisite to understanding this particular developmental programme.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01002715
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