**Bone of Forelimb: Humerus**

The bone of the forelimb is the humerus. The humerus is the long bone located in the upper arm or forelimb of humans and other animals. It connects the scapula (shoulder blade) to the radius and ulna (lower arm bones). The humerus plays a crucial role in the movement and support of the arm.

**Function of the Humerus:**

1. **Support and Structure:** The humerus provides structural support to the upper limb, allowing for movement and stability. It acts as a framework for muscles, tendons, and ligaments to attach, facilitating the movement of the arm.

2. **Articulation:** The humerus articulates with the scapula at the shoulder joint and with the radius and ulna at the elbow joint. These articulations allow for the movement of the arm in various directions, such as flexion, extension, adduction, abduction, and rotation.

3. **Muscle Attachment:** The humerus serves as an attachment site for several muscles involved in arm movement. Muscles such as the deltoid, biceps brachii, triceps brachii, and brachialis attach to the humerus, allowing for the contraction and movement of the arm.

4. **Blood Supply:** The humerus contains nutrient foramina, which are small openings that allow blood vessels to supply oxygen and nutrients to the bone. These blood vessels help nourish the bone cells and promote bone growth and repair.

**Structure of the Humerus:**

The humerus is a long bone that consists of several anatomical features:

1. **Head:** The head of the humerus is located proximally and articulates with the glenoid cavity of the scapula, forming the shoulder joint.

2. **Greater and Lesser Tubercles:** These bony projections are located on the anterior aspect of the humerus and serve as attachment sites for muscles and tendons of the rotator cuff.

3. **Shaft:** The shaft of the humerus is the long, cylindrical part of the bone, extending from the head to the distal end. It provides support and stability to the upper limb.

4. **Medial and Lateral Epicondyles:** These bony prominences are located at the distal end of the humerus and serve as attachment sites for muscles and ligaments of the elbow joint.

5. **Capitulum and Trochlea:** These are two articulating surfaces located at the distal end of the humerus. The capitulum articulates with the radius, while the trochlea articulates with the ulna, forming the elbow joint.

In conclusion, the humerus is the bone of the forelimb, connecting the scapula to the radius and ulna. It provides support, structure, muscle attachment, and facilitates movement in the upper limb.