The report of the M. pyramidalis was studied in 51 cadavers of Korean adults (male 33, female 18). Origin, insertion and number of this muscle were observed, and the length and breadth were also measured. The results were as follows : 1. The right pyramidal muscle was absent in one male cadaver, and the left pyramidal muscle was absent in two male cadavers. 2. In one male cadaver, pyramidal muscles of both sides had bifurcated origin. 3. In Korean adults, the average length of this muscle was 6.72cm in right, 7.05cm in left, and the breadth was about 2.0cm in both sides. The morphological index was 31.10 in right, and 29.55 in left. 4. In Korean male, the average length of this muscle was 1.93cm in right, 7.42cm in left, and the breadth was 1.93cm in right and 1.92cm in left. The morphological index was 28.70 in right and 26.58 in left. 5. In Korean female, the average length was 6.26cm in right, 6.38cm in left. and the breadth was 2.13cm in right and 2.12cm in left. The morphological index was 35.57 in right and 34.63 in left. 6. Compared with other human races, the pyramidal muscle was less frequently wanting in Asians (3.9%), including the Korean adults, than wanting in European (19.9%), American Whites (20.4%) and Negroes (15.1%). 7. The morphological index of this muscle was little differences existing in male of the human races, but this index was higher in Korean female (35.0) than in Japanese female (24.4) and in American female Whites (25.8). The morphological index was 32.3 in American female Negroes.