The reinforcements are beginning to arrive.

The 49ers, who practiced with only five healthy defensive linemen in Maryland recently, on Tuesday removed nose tackle Ian Williams from the physically-unable-to-perform list. Williams, 24, was San Francisco's starting nose tackle early last season but suffered a nasty lower leg injury when a Seahawks offensive linemen cut-blocked him in Week 2. That type of block -- from the side, with the offensive lineman rolling up the leg -- will be penalized this season.