The epiphysis is the expanded end portion of a long bone, such as an arm or leg. It articulates or forms a joint with another bone. On its outer surface, the articulating portion of the epiphysis is coated with a layer of hyaline cartilage called articular cartilage. The epiphysis, are composed of largely spongy (cancellous) bone with thin layers of compact bone on their surfaces. Spongy bone provides strength and its bony plates are most highly developed in the regions of the epiphyses that are subjected to forces of compression.