Forearm Forearm The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in anatomy, technically, means only the region of the upper arm, whereas the lower "arm" is called the forearm. It is homologous to the region of the leg that lies between the knee and the ankle joints, the crus. The forearm contains two long bones, the radius and the ulna, forming the radioulnar
Bone A bird's beak is primarily made of bone as projections of the mandibles which are covered in keratin. A deer's antlers are composed of bone which is an unusual example of bone being outside the skin of the animal once the velvet is shed. The extinct predatory fish "Dunkleosteus" had sharp edges of hard exposed bone along its jaws. Many animals possess an exoskeleton that is not made of bone. These include insects and crustaceans. The proportion of cortical bone that is 80% in the human skeleton may be much lower in other animals, especially in marine mammals and marine