The thick, soft muscles, which lie close under the backbone in the small of the back, in all animals, have less of this tough and indigestible fibrous stuff in them, and cuts across them give us the well-known porter-house, sirloin, or tenderloin steaks, and the best and tenderest mutton and pork chops.
Fuel Value of Meats.

Weight for weight, most of the butcher's meats--beef, pork, mutton, and veal--have about the same food value, differing chiefly in the amount of fat that is mixed in with their fibres, and in certain flavoring substances, which give them, when roasted, or broiled, their special flavors.

The different flavors are not of any practical importance, except in the case of mutton, which some people dislike and therefore can take only occasionally, and in small amounts.
The amount of fat in meats, however, is more important; and depends largely upon how well the animal has been fed.

There is usually the least amount of fat in mutton, more in beef, and by far the greatest amount in pork.

This fat adds to the fuel value of meat, but makes it a little slower of digestion; and its presence in large amounts in pork, together with the fact that it lies, not only in layers and streaks, but also mixed in between the fibres of the lean as well has caused this meat to be regarded as richer and more difficult of digestion than either beef or mutton.