The fluid flow dynamics in the developing chick wing.

The results of previous studies on the temporal sequence of limb vascularization suggest that prospective morphogenetic areas of the limb are distinguished by a differential vascularization pattern prior to the overt expression of distinctive phenotypes (Evans, 1909; Caplan and Koutroupas, 1972; Feinberg and Saunders, 1982). The experiments presented here reveal the dynamic aspects of limb vasculogenesis by detailing how a particulate tracer, india ink, is dispersed by the complex vascular tree. Data are presented as a temporal sequence of fluid flow maps which indicate the direction and specific rate of vascular flow in the limb. Our observations suggest that the limb is subcompartmentalized into discrete microenvironments that are spatially distinct with regard to their capacity for transporting a particulate tracer. The developmental significance of these observations may be that limb mesenchymal cells are granted precise "positional information" in the form of the specific nutrient and oxygen levels they encounter during critical phases of limb morphogenesis.