[Vessel work development phases in the neural part of the pons in chick embryos]

By means of intravascular India ink injections we have analyzed the early developmental phases of the vessel network in the cranial part of the chick embryo pons. At four and one half days of incubation the first radial endoneural vessels have already entered the ventral portion of the pons and formed with their branches a perigerminative network. Both the external and deep network progressively extend during the subsequent days, and at the 7th day the previously segregated cell groups begin to be encircled by tiny branches from the radial vessels. On the 8th day vessels appear also within the cellular groups and differences in vascular density between the various groups become detectable, apparently depending on their different cell density and differentiation degree. From this stage until the 12th day the vessel denseness undergoes a gradual, general increase, although differences in the vascularization degree between various groups are still appreciable.