I'm still looking up all those
Words he used in the post?
Using the right words ensures that there is no confusion.
Retroperitoneal: outside of the abdominal cavity. The peritoneum is the clear membrane that lines the inside of the abdomen. Everyone's heard of peritonitis, an inflammation of the peritoneum. The tenderloin--as well as the kidneys--are outside of this membrane.
Proximal: closer, as toward the head. Cranial.
Distal: farther way, as toward the tail. Caudal.
Lumbar vertebrae: the 7 (usually) backbones that lie between the ribs and the pelvis. When you strain your back while lifting something, you usually hurt your lumbar area.
Tranverse processes. Anyone who has seen bleaching bones out in the field will note that most vertebrae have a single dorsal process sticking up and two transverse processes that flare out to the left and right. The long bone in a T-Bone steak is a transverse process. It separates the backstrap above from the tenderloin below. Next time you pet your dog, feel along his back in front of his pelvis. You can actually feel the muscle-covered transverse processes on each side. Imagine making an incision from his ribs to his pelvis right over the ends of these processes. Then imagine working your hand on the bottom side of the processes to work the muscle away from the bone above.
That's it!