Abstract: The sternoclei domastoid and trapezius muscles of the rabbit were separately injected by CT-HRP in order to trace their original neurons in the spinalcord. The results showed that the sternocleidomastoid and trapezius motoneurons were localized in two distinct cell columns in the ventral horn of the cervical spinal cord, The sternocleidomastoid motoneurons were found in a dorsomedial position of the ventral horn in C₁ and C₂, mostly distributed in caudal C₁ and rostral C₂ segments. The mean diameter of the soma was 36.7μm. The trapeziut motoneurons wre found in a ventrolatral position of the ventral horn in C₂ ～ C₅, mostly located in C₃ and C₄ segments. The mean diameter of the soma was 29.3μm, slightly smaller than those of the ster nocleidomastoid motoneurons. The dentrites of the sternocleidomastoid and trapezius motoneurons were extentively distributed in the gray matter and extended into the white matter. The dentrites of the sternocleidomastoid motoneuront were especially distributed to the central gray. The results provided a morphological foundation for ditcussing the functional differences between the sternocleidomastoid and trapezius muscles.

Key words: sternocleidomastoid and trapezius muscles, motoncurons, spinal cord, CT-HRP, rabbit