In this lecture, Professor Diamond continues her discussion of human muscle systems by describing the muscles of the arm and forearm as well as the abdominal muscles.  She begins by describing the origin and insertion of the tricep and brachioradialis. She discusses forearm muscles generally, grouping them into flexors and extensors. Next, Professor Diamond describes four abdominal muscles, relating their names to the ways in which they cross the abdomen. She describes how working out increases the tendinous inscriptions between the abdominal muscles and also reveals how common inguinal hernias occur. Professor Diamond notes that the abdominal muscles have many functions, including support, protecting viscera, flexing vertebral column, breathing, vomiting, laughing, coughing and sneezing, and defecating. She concludes by discussing the muscles of the pelvic floor and the muscles of the hip, including the gluteal muscles.