The tough structures that hold the bones together at the joint are called ligaments.

Ligaments are strong bands of fibrous connective tissue that connect bones to other bones, providing stability and support to the joints. They play a crucial role in maintaining the integrity of the skeletal system and allowing smooth movement between bones.

Function of Ligaments:
1. Stability: Ligaments help stabilize the joints by limiting excessive movements. They prevent the bones from dislocating or moving out of their normal range of motion.
2. Support: Ligaments provide support to the joints, especially in weight-bearing joints such as the knees and ankles. They help distribute the body's weight evenly across the joints, reducing the risk of injury.
3. Flexibility: Ligaments allow for controlled and coordinated movements of the joints. They provide the necessary flexibility for various activities such as walking, running, and bending.
4. Shock absorption: Ligaments help absorb and distribute forces applied to the joints, protecting the bones from excessive stress and impact.

Structure of Ligaments:
Ligaments are composed of dense, fibrous collagen fibers. These fibers are arranged in a parallel or crisscross pattern, giving the ligaments their strength and flexibility. The collagen fibers are embedded in a gel-like substance called the extracellular matrix, which provides additional support and nourishment to the ligaments.

Types of Ligaments:
There are different types of ligaments in the human body, classified based on their location and function. Some common types include:
1. Capsular ligaments: These ligaments surround the joint capsule, providing stability and preventing excessive movement.
2. Intracapsular ligaments: Found inside the joint capsule, these ligaments help stabilize the joint and control its movements.
3. Extracapsular ligaments: These ligaments are located outside the joint capsule and provide additional support and stability to the joint.
4. Intraligamentous ligaments: These ligaments are located within the substance of a specific ligament and provide reinforcement to it.

Conclusion:
Ligaments are essential structures that hold the bones together at the joints. They provide stability, support, flexibility, and shock absorption to the joints, allowing for smooth and controlled movements. Understanding the role and structure of ligaments is crucial in maintaining joint health and preventing injuries.