The orientational projections of sensory fibres of median nerve to the Substantia Gelatinosa (SG) of the spinal cord in rats were studied in accordance with the principle of transganglion degeneration by using the acid phosphatase technique. It was found longitudinally that the afferent fibres of the median nerve projected chiefly to SG from the upper part of C_5 to middle part of T_1. In a few rats, projections extended to middle and lower part of C_4 and lower part of T_1. In comparison with the records in anatomy literature and data from researches with HRP technique, a tendency of pre-positioning was noted. The regional projections of the afferent fibres of median nerve were found within the centre line of SG, and mainly in the region of the medial 1/4-1/2 of the medial half. In the segments of C_7-T_1 of a few rats, the whole area of the medial half of SG was projected. In observing the projections of the afferent fibres of median nerve, it was found that they have a tendency of lateralward increase from cranial portion to caudal portion.

The orientational projections of sensory fibres of radial nerve and ulnar nerve to the substantia gelatinosa(SG) of the spinal cord in rats were studied in accordance with the principle of transganglion degeneration by using the acid phosphatase technique.It was found that the affeernt fibers of the radial nerve projected chiefly to SG, from the upper part of C_6 to the middle part of T_1 longitudinally; the ulnar nerves projected chiefly to SG from the middle part of C_6 to the middle part of T_1.In their transverse projections,the afferent fibres of the radial nerve were mainly found in the region of the whole area of the middle 1/3 of SG; and the afferent fibres of ulnar nerve were found within the centre line of SG, and mainly in the region of the lateral 1/2～3/4 at medial half. In summary, radial nerve projected to the lateral region and ulnar nerve to the medial region of SG.

The orientational projections of the sensory fibres of axillary nerve to the substantia gelationsa (SG) of the spinal cord in rats were studied in accordance with the principle of transgangionic degeneration by using acid phosphatase technique. It was found that the afferent fibers of the axillary nerve projected chiefly to SG from the upper part of C_6 to the lower part of C_8 longitudinally. In a few rats, projections extended to the lower part of C_5 and upper part of T_1. In comparison with the available studies, a tendency of backward localization was noted. As to their transverse projections, the afferent fibres of the axillary nerve were found outside of the midline of SG, and mainly located in the lateral half of SG, at the 1/3 of median and the 1/3 of interior region. In the segments of C_7C_8 of some rats, the medial. 1/2 of the lateral half of SG was projected. It was found that the projection column from up downward had a tendency of extension toward lateral portion.