Which statement about stay apparatus across species is true?

Which statement about stay apparatus across species is true?

• A. Horses have no stay apparatus
• B. Horses have highly developed stay apparatus with prominent reciprocal mechanism and suspensory system; ruminants have a less specialized but present stay mechanism
• C. All ruminants have identical stay apparatus to horses
• D. Stay apparatus is only seen in birds

Answer: (B)

Stay apparatus is a system of joints, ligaments, and tendons that lets a limb bear weight in extension with minimal muscular effort. In horses this is highly developed and relies on a prominent reciprocal mechanism that coordinates the forelimb and hind limb segments so that movement in one part is matched by a lengthening or tightening in another, plus a strong suspensory apparatus that keeps the fetlock extended. This combination enables the horse to stand quietly for long periods with little muscular work, which is advantageous for grazing and watchfulness. Across species, this mechanism exists but to varying degrees: ruminants have a stay apparatus as well, but it is less specialized than in horses. The other statements don’t fit because horses do have a stay apparatus, not all ruminants have identical systems to horses, and the concept isn’t limited to birds.

Stay apparatus is a system of joints, ligaments, and tendons that lets a limb bear weight in extension with minimal muscular effort. In horses this is highly developed and relies on a prominent reciprocal mechanism that coordinates the forelimb and hind limb segments so that movement in one part is matched by a lengthening or tightening in another, plus a strong suspensory apparatus that keeps the fetlock extended. This combination enables the horse to stand quietly for long periods with little muscular work, which is advantageous for grazing and watchfulness. Across species, this mechanism exists but to varying degrees: ruminants have a stay apparatus as well, but it is less specialized than in horses. The other statements don’t fit because horses do have a stay apparatus, not all ruminants have identical systems to horses, and the concept isn’t limited to birds.