DEVELOPMENT OF NERVES IN THE UPPER LIMB OF HUMAN EMBRYOS

Abstract

Nerve innervation is important for normal development of the limb in the laboratory animals. There are only few reports on the morphogenesis of nerves in the upper limb of human embryos. In this study 20 cases of staged human embryos between Carnegie stage 11 and 23 were used to pursue the chronological relationships between the nerves and the skeleton and muscles in the developing human upper limb. Formalin-fixed embryos were dehydrated with graded alcohol, cleared with histoclear, and embedded in paraffin. Serial sections were stained with hematoxylin-eosin and trichrome. Three dimensional reconstruction models had been prepared by tracing on the blotting papers. The upper limb bud appeared at stage 12, and regularly developed during embryonic period. Primitive brachial plexus was formed at stage 14, but did not reach the limb bud. Brachial plexus entered the upper limb bud at stage 15, and branched into major nerves. Major nerves had branches at stage 17. Branches grew distally as the limb bud developed, and reached distal phalanges at stage 23.