Police in Somerville found human remains along the train tracks near School Street Sunday afternoon, the Middlesex district attorney’s office said. Stephanie Guyotte, a spokeswoman for Middlesex District Attorney Marian T. Ryan, said she could not elaborate on the nature of the remains. Somerville police and State Police assigned to Ryan’s office were investigating the discovery. Guyotte would not say whether foul play was suspected. The remains were found about 12:45 p.m., according to a statement from Ryan’s office. The MBTA Lowell commuter rail line runs along the tracks.