Largest sesamoid bone of the body.

Lies in: Tendon of insertion of QUADRICEPS FEMORIS muscle.

Articulates with: Trochlea (patellar groove) of femur.

Shape (Ox): Rounded, somewhat 4-sided; thick.

Functions:
- Increases the leverage of quadriceps for stifle extension.
- Protects the front of the stifle joint.

3 Patellar Ligaments hold it down to the tibia (in horse, ox): Medial, Middle, Lateral patellar ligaments.

Special: Parapatellar fibrocartilages on medial and lateral sides — extend the patellar surface.

PATELLA — THE KNEE CAP

The patella is the largest sesamoid bone in the body. It develops within the tendon of the quadriceps femoris muscle and acts like a pulley — it lifts the line of pull of the quadriceps away from the joint, giving the muscle better leverage to extend the stifle.

SHAPE in OX: Roughly four-sided (rhomboidal) with a thick cranial face and a smooth caudal face that glides over the trochlea of femur.

SUPPORTING LIGAMENTS:
In horse and ox there are three patellar ligaments that anchor the lower end of the patella to the tibial tuberosity:
• Medial Patellar Ligament
• Middle (Intermediate) Patellar Ligament
• Lateral Patellar Ligament
(In dog & pig there is essentially one — 'patellar ligament' or 'straight patellar tendon'.)

PARAPATELLAR FIBROCARTILAGES: On either side of the patella in horse and ox, projecting downward — they extend the contact surface and are crucial in the equine 'stay apparatus' (the medial parapatellar fibrocartilage hooks over the medial trochlear ridge).

FUNCTION:
1. Improves leverage of quadriceps → strong stifle extension.
2. Protects the front of the stifle.
3. In horse — used for the stifle lock (the medial patellar ligament + medial parapatellar fibrocartilage catches over the medial trochlear ridge so the horse can stand and sleep without muscular effort).