Final answer:
The suspensory ligament in horses is also known as the interosseous muscle, a critical component in supporting the fetlock joint and preventing overextension during movement.
Step-by-step explanation:
The suspensory ligament in the horse is also known as the interosseous muscle (third or modified part), which has evolved through the course of evolution from being a muscle to becoming a ligament. Its primary function is to support the large metacarpal or metatarsal phalangeal joint, thus playing a critical role in the horse's ability to stand and move efficiently.
This ligament originates from the back of the cannon bone's upper part and then divides into two branches, which attach to the sesamoid bones at the back of the fetlock joint. Each of these branches further divides to attach to the long pastern bone (P1) and the short pastern bone (P2). The suspensory ligament is vital for the equine's limb mechanics, as it helps to prevent overextension of the fetlock when the horse's foot impacts the ground during locomotion.