"There was a gunshot wound entrance over the left lower lateral (lower left ribs) chest wall and the bullet could be felt in the subcutaneous tissue (beneath the skin) on the opposite side of the body, over the right lower lateral chest cage."
Dr. Thomas Shires, Chief of Surgery, Parkland Hospital
In the autopsy that followed, this was said about the entrance wound: "It is found to notch the undersurface of the seventh rib at the costochondral junction."
Below, I have counted down the ribs from the top. The costo-chondral junction is where the big piece of cartilage which connects the rib to the sternum connects to the bony rib. In the diagram below, the cartilage is colored tan and the bony rib is colored grey, to distinguish them. Oswald got hit at the undersurface of the seventh rib at the costochondral junction. It is marked with a small x and circled. That is where the bullet went in, not through the soft belly.