The San Francisco 49ers signed cornerback Kris Richard and put running back Kevan Barlow on injured reserve Wednesday with a lingering knee injury. Barlow has missed three of the 49ers' last four games, including Saturday's victory at St. Louis, where Maurice Hicks and rookie Frank Gore combined for 177 yards rushing and three touchdowns. Barlow finished the season with 581 yards rushing, averaging just 3.3 yards per carry, and three touchdowns, disappointing numbers for a running back whose job security was in jeopardy when the 49ers were in the running for the top overall draft pick, expected to be USC running back Reggie Bush. Richard was a backup in Seattle for three seasons before getting traded to Miami in training camp. The Dolphins cut him before the regular season began. The 49ers (3-12) needed immediate help in the defensive secondary before their regular-season finale Sunday against Houston (2-13) at Candlestick Park. Five cornerbacks -- starters Shawntae Spencer (quad) and Bruce Thornton (knee), along with rookie Derrick Johnson (stinger), B.J. Tucker (finger) and benched veteran Ahmed Plummer (ankle) -- might be unavailable because of injuries.