PROGRESS OF MYELINIZATION IN THE EIGHTH CRANIAL NERVE GANGLION OF THE CHICK.

It has been repeatedly described since the middle of last century that, like nerve fibers, the very perikarya of certain sensory ganglion cells are also enclosed in myelin (M u n z e r, '31 ; S c h a r f, '58). Such myelinated neurons appear predominantly in the eighth cranial nerve ganglia of man and the vertebrate animals. As for the avian materials, the presence of the myelinated neurons in the eighth cranial nerve ganglia of hen, Gallus domesticus (M il n z e r, '31) and sparrow, Passer domesticus (S char f, '51) has also been reported so far. The progress of myelinization around these nerve cell bodies in the ontogenetic process is of interest not only from the morphological viewpoint but also from the physiological, since it may be closely related to the functional development of the cells. However, the chronology of perikaryal myelinization in any vertebrate has not been clarified yet. The present study was projected to examine when the myelin formation does occur in the developing chick.