Stay apparatus

The stay apparatus is an arrangement of muscles, tendons, and ligaments that work together so that an animal can remain standing with virtually no muscular effort.

The relatively slim legs of certain large mammals, such as horses and cows, would be subject to dangerous levels of fatigue if not for the stay apparatus.

[2] The upper portion of the stay apparatus in the forelimbs includes the major attachment, extensor, and flexor muscles and tendons.

[4] In essence, the accessory check ligaments act as tension bands, they stabilize the carpus (called the "knee" in horses), fetlock and bones of the foot.

The medial patellar ligament "locks" the patella ("kneecap") in place and this prevents flexion in both the stifle and the hock.