Bone still cartilaginous. The following steps are followed in the conversion of cartilage to bone: Bones have a variety of functions: Bones serve a variety of mechanical functions. Together the bones in the body form the skeleton. They provide a frame to keep the body supported, and an attachment point for skeletal muscles, tendons, ligaments and joints, which function together to generate and transfer forces so that individual body parts or the whole body can be manipulated in three-dimensional space (the interaction between bone and muscle is studied in biomechanics). Bones protect internal organs, such as the skull protecting the brain
Skeletal muscle "flexor" and "extensor"; "abductor" and "adductor"; "levator" and "depressor"; "supinator" and "pronator"; "sphincter", "tensor", and "rotator" muscles. A flexor muscle decreases the anterior angle at a joint; an extensor increases the anterior angle at a joint. An abductor moves a bone away from the midline; an adductor moves a bone closer to the midline. A levator raises a structure; a depressor moves a structure down. A supinator turns the palm of the hand up; a pronator turns the palm down. A sphincter decreases the size of an opening; a tensor tenses a body part; a rotator turns a bone around