Many years ago, dog breeders and enthusiasts were also skilled horsemen. 

They knew exactly what bone and body structure was needed to build a strong dog who wouldn’t break down doing the job it was bred for. 

This is because horses with the best structure (conformation) got injured the least, could do the most work without tiring, and were the most comfortable to ride!

Some of these horsemen helped write Standard descriptions for their dog breeds.

This is why many body part names are the same for dogs and horses.