Directly from downward dog in the previous sequence of movements.
Vinyāsa 7: Inhale, Exhale, Inhale:
Inhale from downward dog as you slide your legs through and balance on your hands. Exhale and lower yourself down slowly between your arms . Place your left leg in lotus position and then set the right foot down with a bent knee just as you did in Marīchyāsana A. Inhale and wrap the right arm around the shin and grasp the left hand. Inhale and lengthen the spine.
Note: To protect your left knee from unnecessary pressure, there are two things to take into consideration. First, place the left foot as close as possible to the trunk in lotus so that the right leg does not raise the foot any further. Then tilt your pelvis to the left at the same time that your right foot is drawn up so that the left thigh maintains contact with the floor. This will keep the left knee in stabile alignment.
Vinyāsa 8: Exhale, 5 Breaths:
Exhale and lower the torso down until your chin reaches the floor on the inside of the left knee. Your gaze moves forward to between the eyebrows. Stay here until the fifth exhalation.
Note: The the traditional form of Aṣṭāṅga Yoga we always start on the right and then move to the left side. With a simple rule you can easily recall which side is the right side (first to be executed):
“Right side comes first, means right leg moves last"
In the example of Marīcyāsana B the pose is only realistically possible by pulling the right leg up after setting the left in lotus. The raised leg is thus on 'top' and is can be defined as the right side.
Vinyāsa9: Inhale, Exhale
Inhale and lift the torso without loosening the bind. Stay here for a long exhalation.
Vinyāsa 10 to 13:
Follow the flow of movements that you already know up to downward dog.
Vinyāsa 14 to 20:
Repeat the sequence of movements on the second side until you are again in downward dog.
In the traditional count, change here directly into the flow of movements of the next posture.
Effect: The left foot being placed in lotus creates a small distance between the origin of the right thigh and the pelvis. This creates outward directed tension on the hip joint. For the right leg, which is placed similarly to Marīcyāsana A, unwinds the joint capsule of the hip. This pull enlarges the area of the joint which allows the cartilage to absorb more nutrients.