When you’re married to a veterinarian you learn all sorts of things that you’d probably never learn otherwise. One of those things is that dogs (and most of our other four-legged friends) don’t have the number of knees that most people think they do.
How many knees does a dog have? Two. They also have two elbows, and it’s not just a semantic thing. A dog’s front legs are built more like a human arm than a leg, complete with a shoulder (not hip), humerus, radius and ulna. The rears leg are attached to the pelvis and include a femur, fibula and tibia, as well as a patella which I’m pretty sure is a kneecap.
So there you have it- dogs have two knees even though we say they have four legs. For the record, Miller’s Anatomy of the Dog (which happens to be on the bookcase in our home office) refers to them as limbs, not legs, but dictionary.com says that a leg is “any of the paired limbs of an animal, arthropod, etc., that support and move the body.” So by that definition dogs (and most other four-legged animals I presume) have elbows on their front legs.
Feel free to use this to mess with your friends. I suppose it’s common sense to people that have a good understanding of anatomy, but most of us either don’t or don’t spend a whole lot of time thinking about it.