In this image made from video provided by Vicki Black, Ariel is seen with six legs before surgery, in Bristol, England. AP

Ariel, who was named for "The Little Mermaid” character because the additional appendage with two paws on the end looked a flipper, ran through the grass on Saturday as she adjusted to life on four legs.

"She is doing brilliantly,” said Vicki Black, director of the Langford Vets Small Animal Referral Hospital, where she was operated on Thursday.

The dog, who had multiple birth defects, was found in the centre of Pembroke, Wales, in September. Greenacres Rescue took her in and raised funds for her surgery.

Black said the hospital, which is part of the University of Bristol, had never seen a six-legged dog or performed such an operation.

"Ariel was a complicated little dog,” Black said. "We are a center committed to career-long learning and are proud to innovate and treat pets like Ariel.”

The extra legs extended from the right hindquarter and appeared to be of no use, dangling beside her wagging tail, as she walked a bit awkwardly in a video shot before the operation.

On Saturday as she was discharged, she took to the lawn outside the hospital with the determination of a bird dog, nose to the ground and pulling on her leash.

Associated Press