Lynn Poole and models Dick Manson and Barbara Casey demonstrate how bones and muscles function with our actions. Dr. William Montagna, professor of biology at Brown University, looks at bones from an artistic point of view. He displays the lumbar vertebrae of both a whale and a human and notes their structure. He contrasts the humerus from the upper arm, the scapula from the shoulder, and the carpal bones of the wrist. Comparing the skulls of a man and a woman, Dr. Montagna explains the differences. The three types of joints he lists are the fused in the skull, the hinge-type in the elbow, and the ball and socket in the shoulder and hip. Investigating the interior of bones, Dr. Montagna shows the frontal sinuses of the head and compares the spongy bone material at each end of a bone to a bridge structure. For strength and resiliency, bones require both organic and inorganic substance, which Dr. Montagna demonstrates with bones lacking one or the other. A diagram shows how the endosteum and the periosteum balance bone growth. X-ray films compare the hands of a three-year-old, which has cartilage at the end of each bone, and a thirty-year-old, which has bone in place. Dr. Montagna concludes that bone is a living tissue, as evidenced by its mechanism to repair itself quickly.