Anatomy Guide › Upper limb
Humerus
The humerus is the single long bone of the upper arm and the largest bone of the upper limb. At its top, a smooth hemispherical head fits into the shallow socket of the shoulder blade, forming the most mobile joint in the human body — you can swing your arm through nearly a full sphere because the socket is so shallow and the capsule so loose. That freedom has a price: the shoulder dislocates more often than any other major joint, and it is almost always the humeral head that pops out.
The shaft of the humerus is a highway lined with muscle attachments. The deltoid grips a roughened patch halfway down its outer surface; the pectoralis major and latissimus dorsi anchor near the top; and at the bottom the bone flares into the paired knobs you feel on either side of your elbow. Between shaft and knuckles winds one of anatomy's best-known hazards: the radial nerve spirals in a groove directly on the bone. A mid-shaft fracture can stretch or cut it, producing 'wrist drop' — the hand hangs limp because the muscles that lift it lost their signal.
The lower end of the humerus forms the elbow with the radius and ulna: part pulley, part ball, allowing both hinge bending and the forearm's rotating motions. The 'funny bone' zing when you knock your inner elbow is not the humerus itself but the ulnar nerve pressed against its inner knob — another nerve that treats this bone as scaffolding.
In Anamo, the humerus is the backbone of the upper-limb map. It touches shoulder muscles above, forearm bones below, and major vessels and nerves along its length, so its heat reading orients almost any arm-region round.
- Forms the most mobile joint in the body at the shoulder
- The radial nerve spirals in a groove directly on its shaft
- The 'funny bone' sensation comes from the ulnar nerve at its inner elbow knob
- Largest bone of the upper limb
Think you could find the humerus on a 3D model? Play Anamo and test yourself — every guess is color-coded by how close it lands to the mystery structure.