The anterior meniscofemoral ligament or ligament of Humphrey is a small fibrous band of the knee joint. It arises from the posterior horn of the lateral meniscus

Lateral meniscus

The lateral meniscus, also called the external semilunar fibrocartilage, is a fibrocartilaginous band that spans the lateral side of the interior of the knee joint. It is one of two menisci of the knee, the other being the medial meniscus. It is nearly circular and covers a larger portion of the...

 and passes superiorly and medially in front of the posterior cruciate ligament

Posterior cruciate ligament

The posterior cruciate ligament is one of the four major ligaments of the knee. It connects the posterior intercondylar area of the tibia to the medial condyle of the femur...

to attach to the lateral surface of medial femoral condyle.
It may be confused for the PCL during arthroscopy. In this situation, tug on the ligament while observing for motion of the lateral meniscus;