Apprentice jockey Terri Canary fractured a vertebra in a fall at Laurel yesterday, and in separate incidents journeymen Gregg McCarron and Joe Rocco were injured before their horses had a chance to leave the starting gate.

Canary, 20, went down in a frightening spill in the second race when Fleetwood Hill broke both forelegs near the far turn. The filly pitched Canary forward and rolled over her.

Canary, who broke her pelvis in 1986 when a pleasure pony reared and fell on her, was X-rayed at Howard County General Hospital, where she stayed the night. Fleetwood Hill, a 3-year-old claiming filly making her 13th start, was destroyed.

Although Canary is familiar on the Maryland circuit, she's been riding primarily at Penn National the past few months, where she ranks 12th in victories. She faces a long recovery.

McCarron broke the third metacarpal bone in his left foot when Casement, a 70-1 shot, became agitated and fell in the starting gate before the seventh race. McCarron was scheduled to ride the favorite in a $40,000 stakes race today, but will be out three to six weeks.

Rocco bruised the left heel he broke last year when Working Late unseated him during the third-race post parade. Rocco took the rest of the afternoon off.

Flaming Emperor Hot

Flaming Emperor, who has blossomed into the finest Maryland-bred handicap horse of 1990, will try for his fourth straight victory in the Baltimore Breeders' Cup today at Laurel. The $75,000-added race awards an additional $100,000 to Breeders' Cup-nominated horses, who do not include Flaming Emperor.

The 1 1/8-mile race attracted a field of six, including Doc's Leader and Finder's Choice.

Earlier on the 12-race program (which includes a simulcast of the Caesars International Handicap), nine fillies will try the $40,000-added Toddler Breeders' Cup Stakes, Maryland's first stakes race for 2-year-olds in 1990.

Trainers Bernie Bond and Carlos Garcia entered two fillies each. Bond's Gala Goldilocks -- the horse McCarron was to have ridden -- is the program favorite; Garcia's Devilish Touch, an unraced daughter of Devil's Bag, reportedly is one of the trainer's fastest 2-year-olds.

Garcia has other pressing matters on the New Jersey shore with Valay Maid running in the $150,000 Monmouth (Park) Oaks. . . .

After three weeks of operation, Pennsylvania's first off-track betting facility is handling almost twice as much as expected, according to Ladbrokes, the British-based company that operates it.

Wagering at the OTB center, in New Castle near the Ohio border north of Pittsburgh, is said to be averaging about $100,000 per day, $46,000 above projections. The facility simulcasts races from the state's four tracks, thoroughbred and harness.

New Castle is the first of 23 OTB centers to be built in Pennsylvania by 1995; a facility is scheduled to open in Philadelphia next month. Pennsylvania's OTB success is of keen interest to Maryland racing officials because it could draw from their market. Although it perceives Pennsylvania as a threat, Maryland has lagged in pursuing OTB legislation.