The tenderloin, as with all quadrupeds, refers to the psoas major muscle, which is located ventral to the transverse processes of the lumbar vertebrae, near the kidneys. The tenderloin is an oblong cut that spans two primal cuts: the short loin and the sirloin. The tenderloin is located beneath the ribs, near the backbone. Because this muscle does very little work, it is the most tender part of the beef.