what made Dr Mortimer belive in the hound

Dr. Mortimer explains that he has brought a manuscript, but Holmes has already observed it in his pocket, and surmises aloud that it is from the early eighteenth century. The manuscript details how thirteen men followed Hugo, who was ahead of them. They encountered a shepherd who was "crazed with fear" - he had seen the maiden, but had also seen a "hound of hell" in fast pursuit of Hugo (148). Eventually, the men encountered Hugo's mare, alone and frothing at the mouth. Frightened, they persevered until they came across a trench, next to which the hounds were whimpering. In the trench, three of the men found the maiden, dead "of fear and of fatigue", and Hugo, dwarfed by a "great, black beast, shaped like a hound" (148). The giant hound tore Baskerville's throat out, at which point the men fled. One of the men died that night, while the other two remained "broken men" for the rest of their days (149).