Ligaments, and sometimes even tendons
The humerus is a bone in the upper arm that has a long longitudinal axis with expanded ends where it articulates with the scapula at the shoulder joint and the radius and ulna at the elbow joint.
Ligament is what holds a bone to a bone
cartilage
Ligaments connect bones to bones. Muscles are connected to bone by tendons.
The capsule of the joint holds the bone ends together. The capsule is mainly composed of collagen fibers. The capsule is tight enough to hold the bone ends. Loose enough to permit the moments of the bones.
The cartilages at the ends of bones act as a soft pliable cushion between the bones that form the joint. Bone on bone movement is very painful.
Bone to bone connections occur by way of ligaments, whereas bone to muscle connections occur by way of tendons.
Hyaline cartilage covers the ends of bones in many joints. It provides a slippery surface to reduce friction during bone movement.
The resilient substance that keeps bone ends from crushing when compressed is called articular cartilage. Articular cartilage is a smooth, elastic tissue that covers the ends of bones in joints, providing cushioning and promoting smooth joint movement.
Dislocation is the injury that occurs when the ends of the bones in a joint are forced out of their normal positions. It can cause severe pain, swelling, and limited range of motion in the affected joint. Treatment usually involves relocating the bones back into their proper position and allowing time for healing.
Epiphyses. (Diaphysis is the middle part). You might also be asking the name of the knobby parts on the ends, which articulate with the next bone and make up the joint: those are 'condyles'.
The cartilage is there to stop bone rubbing against bone. It performs like a lubricant.