Who ran up behind Watson on the road from grimpen to baskerville hall?

In Arthur Conan Doyle's "The Hound of the Baskervilles," it is Sir Henry Baskerville who runs up behind Sherlock Holmes and Dr. John Watson on the road from Grimpen to Baskerville Hall. They are discussing the mysterious events surrounding the Baskerville estate when Sir Henry unexpectedly joins them, adding to the tension and intrigue of the story.