The humerus is the single bone of the upper arm. It belongs to the so-called long bones, which means it has two distinguishable ends — the proximal and distal epiphyses. Both epiphyses are involved in bone growth up to the age of the ossification of epiphysial cartilage. The portion of the bone between these ends is called the diaphysis. Any long bone has two epiphyses and one diaphysis.