VII. On the Proportions and on the Movements of the Human Figure: 356.
356.
Three are the principal muscles of the shoulder, that is b c d, and two are the lateral muscles which move it forward and backward, that is a o; a moves it forward, and o pulls it back; and bed raises it; a b c moves it upwards and forwards, and c d o upwards and backwards. Its own weight almost suffices to move it downwards.
The muscle d acts with the muscle c when the arm moves forward; and in moving backward the muscle b acts with the muscle c.
