The jigot […] is the handsomest and most valuable part of the carcass, and on that account fetches the highest price. It is either a roasting or a boiling piece. Of Black-faced mutton it makes a fine roast, and the piece of fat in it called the Pope's eye, is considered a delicate morceau by epicures. A jigot of Leicester, Cheviot, or Southdown mutton makesa beautiful "boiled leg of mutton," which is prized the more the fatter it is, as this part of the carcass is never overloaded with fat.
Source: wiktionary