A further observation of multiaxonal nerve endings innervating intrafusal muscle fibers of the Chinese hamster.

In addition to annulospiral sensory endings and fusimotor endings, multiaxonal nerve endings consisting of a bundle of naked axons were frequently found in the muscle spindles of the adult Chinese hamster. The multiaxonal endings were mainly distributed in the equatorial region of the nuclear bag fibers, adjacent to the annulospiral sensory endings. Terminal axons composing the endings were less than 1.5 microns in diameter and contained a significant number of clear synaptic vesicles and large granulated vesicles. Some axons formed synaptic contacts with each other and with the muscle cell surface. These structural features suggest that the multiaxonal endings are efferent in nature. They may possibly represent a temporal structure of fusimotor endings, or belong to the autonomic nerves.