Its inferior surface is smooth

. It is the site of the first ossification point.

It is not palpable.

It is formed from one primary and two secondary ossification centers.

The anterior border bears, in its medial third, the deltoid tubercle.

It is located at the anterosuperior part of the thorax.

The medial border is thick because it contains the scapular pillar.

The glenoid cavity is an articular surface with a large cranial extremity.

. It is concave anteriorly.

It is triangular in cross-section.

The humeral head faces upward, medially, and anteriorly.

The proximal epiphysis bears two tubercles.

The deltoid “V” lies on the anteromedial surface.

The medial border gives insertion to the interosseous membrane.

The inferior surface of the distal end of the radius is called the radial tuberosity.

The anterior border extends from the radial tuberosity to the styloid process.

Its shaft has three surfaces: anterior, posterior, and medial.

. Its posterior border, also called the supinator crest, is smooth.

Its anterior surface is divided into two parts by a blunt vertical ridge.

It forms, together with the medially located radius, the skeleton of the forearm.

The lower half of its medial surface is smooth and subcutaneous.

All joints with cartilage have a joint cavity.

Cartilage wear occurs without pain and is irreversible.

All types of joints have a synovial membrane.

Synchondroses and symphyses are cartilaginous joints.

. The glenoid cavity has an irregular concavity.

. The humeral head represents half of a sphere of 30 mm radius.

The sub-deltoid joint is a principal joint of the shoulder.