Postnatal maturation of phrenic, vagus, and intercostal nerves in the kitten.

In the present work, we have compared the histological maturation of the phrenic nerve, the internal and external intercostal nerves of the 8th space and the vagus nerve. At least three nerves from each category have been taken from different kittens each week during the first 2 months of postnatal life, and each month for kittens aged between 2 and 8 months. Compared to references obtained in the adult animal, the development of the number and diameter of myelinated fibers has been studied for each nerve. Moreover, the maturation of unmyelinated fibers of the phrenic nerve has been studied with the electrom microscope. There is a possibility of a cephalo-caudal maturation in the somatic nerves. Important differences exist between somatic nerve maturation and that of the vagus nerve.