An unidentified woman was discovered badly beaten, with her skull cracked, in a Brooklyn alley near train tracks on Thursday morning, cops said.

The victim, who is believed to be in her 40s, was found on Van Sinderen and Liberty avenues at 6 a.m. in East New York, according to police.

Cops found a trail of blood leading from northbound Atlantic Avenue, which is a block away, the sources said.

The victim was rushed to Brookdale Hospital, where she was listed in critical condition, authorities said.

Police are calling the woman “Jane Doe,” because she had no ID. She is 5-foot-8 and 150 pounds.