THE BRACHIAL PLEXUS AND THE WING NERVE PATTERN DURING EARLY DEVELOPMENTAL PHASES IN CHICKEN EMBRYOS

SUMMARY The brachial plexus and the wing nerve pattern have been analyzed at closely spaced time intervals during early developmental phases in chick embryos. The brachial plexus is outlined at 82–84 hr of incubation and it is definitively constituted 36 hr later, as regards differential contribution of the spinal nerves and emergence of peripheral trunks. The spinal nerves XII to XVII participate in plexus formation; the contribution of the XII and XVII nerves is minor but constant. The nerve fibres enter the arm at about 90 hr and the innervation of the arm and forearm is already outlined at the end of the fifth day of incubation. In the hand, innervation begins by the sixth day, reaching the phalangeal region toward the end of the eleventh day. The progress of the wing innervation takes place in a proximo-distal sequence, in parallel with the unfolding of the organogenetic processes of the mesenchymal territories of the bud. The wing nerve pattern attains its definitive arrangement, typical of the adul...