The text explains the detailed workings of various muscles, such as the biceps and triceps, and their roles in different arm movements and positions. It emphasizes how muscles like the Brachieus, Longus, and Brevis should be depicted to show strength and accuracy in art. The descriptions also include muscles associated with lifting and twisting actions, and their relevance to stable figure representation.
Muscles and Their Functions.
To discover the shape with the ribs, it seems we ought to construct it: the renowned painter Amonius Pallaivola undoubtedly observed it well, particularly noted in his powerful drawing of an archer.
If you want to depict a figure lifting a heavy drinking vessel to the mouth, then the arm muscle Brachieus (21) and the two-headed elbow muscle Biceps (22) must be clearly flexed to bend the arm. In a forcefully extended arm that is ready to strike or defend, the muscles Longus (23) and Brevis (24) should both appear elongated as the first, and as the shorter stretcher of arms as the second. This ensures the arm exhibits the required service truthfully. Similarly, a twisting hand, the Longior Supinator (22) or the hand's backward rotator, along with the two extensors or straighteners (32) of the wrist (35) need to swell to twist the hand backward with the knuckles downwards. However, the Round Pronator (34), which turns the hand inward and draws the knuckles down, must work in opposition.
Furthermore, the three muscles Majus (47), Medius (48), and Minimus (49), or the smaller ones, not only compose the buttocks but are also involved in the lifting and straightening of the thighs; therefore, they should prominently feature in stable figures, or those setting their legs firmly against something, giving the illusion of being fleshed out. In the movement of the thigh, the three-headed Triceps muscle (42) turns it inwardly. When the shinbone is perfectly straightened, the muscles Rectus (43), Vastus Externus (44), and Internus (45) are active.
Translation Notes:
Brachieus: Refers to the biceps brachii which are muscles of the arm.
Longior Supinator: Refers to muscles involved in turning movements of the forearm.