This paper studies the participation of vessels in the canal morphogenesis. The proximal chondroepiphysis of the left tibia of 44 five-day-old rats was exposed and the vessels of the intercondylar fossae, near the attachment of cruciate ligaments, were cauterized. In addition to the vascular lesion this assay induced a perichondral lesion. However, the canal appeared and joined to the secondary ossification center. 36 tibiae of 4-day-old rats were removed under sterile conditions and cultured in a serum-free chemically defined medium. The cultures were carried out for as long as 15 days. A canal lumen structure was found on the first days of culture, and grew in depth to the central region of the chondroepiphysis during the culture. The secondary ossification center was not found. The vessels and mesenchymal cells observed in the control canal were not found in the culture. We suggest that the presence of vessels, perivascular cells or perichondrium does not appear to be necessary in canal morphogenesis.

This paper studies the influence of an antimitotic factor (puromycin) and a hormonal factor (thyroid hormone, TH) on canal growth. The tibiae of 15 six-day-old rats were cultured in a serum-free chemically defined medium. The cultures were carried out for as long as 6 days. Our results show: (1) canal growth is not dependent on perichondrium or chondroepiphysis growth; (2) the canal is greater and has a complex pattern in a triiodothyronine (T₃)-treated assay group; (3) round and multinucleated cells are more numerous in the T₃-treated assay group than in the other groups. We hypothesize that the canal grows by a physiological phenomenon of programed cell death and that it is stimulated by TH.

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