Anjaneyasana as a Preparation for Splits
See how the front thigh is moving towards the front calf.
Anjaneya is the name of the mother of Hanuman, the monkey god, who is famous for his giant leap from the southern tip of India to the Himalayas. He performed this incredible feat to save Lakshmana, the brother of Ram, who was wounded in battle. Anjaneyasana is a version of Hanumanasana. You can see the family resemblance in the poses. The thighs are moving towards being 180 degrees from each other. Hanumanasana is a full split and Anjaneyasana is a low and deep lunge.
Malasana - see how the front thigh and calf are together
In Anjaneyasana, you are trying to move the front hamstrings into the back of the calf. This posture in the front leg is similar to the legs in Malasana or Squat. (With the feet sitting bone distance apart) In order to do this, the front knee has to move over the toes of the front foot. As long as your back knee is down on the floor, this is a safe position for the knee. Most students have trouble with this instruction because most of the time we are told to keep the front knee over the ankle. Think that you are trying to get your sit bone to your heel.
See how close Mary's sit bone is to her heel.
The deeper this lunge is, the closer the finger tips will get to the floor. However, it is more important that you keep the hips squared off as you lunge. The hands can rest on blocks or the floor next to your hips. Another factor in getting deeper into this lunge is to keep the chest lifted and not to lean forward over the front leg, but rather, keep your torso centered over your hips.