Final answer:
The inferior rectus muscle is responsible for pulling the eye inferiorly. This muscle is part of the extrinsic eye muscles that control the movement of the eye within the orbit.
Step-by-step explanation:
The muscle that attaches to the anterinferior part of the sclera and pulls the eye inferiorly, as in looking down, is the inferior rectus muscle. This muscle is one of the six extraocular muscles responsible for the movement of the eye within the orbit. In particular, the inferior rectus muscle originates from the common tendinous ring located at the back of the orbit and inserts onto the inferior part of the eye's sclera. When it contracts, it pulls the eyeball downward, allowing us to look down.
Conversely, when the superior rectus contracts, it pulls the eye upward. It's essential to understand that the eyeball's rotation isn't perfectly vertical due to the oblique angle of the muscle insertions. Therefore, the inferior oblique muscle also plays a role in this movement by contracting to rotate the eye laterally, thus helping to align the eyeball correctly as it moves up or down.