This is a beef esophagus (gullet) that has been stuffed with a mixture of ground beef esophagus and wheat flour, with a stretched beef bladder wrapped around. It looks kind of like a bully stick but it's a much softer treat.
These tendons are 6-9" long, of variable thickness, and sourced from free range South American cattle. Tendons are lower in fat compared to other popular chews like marrow bones and pig ears, so they are a good option for dogs with sensitive stomachs.