One of the prominent facial features that I share with my dogs is the presence of a vertical indent between the nose and the upper lip, called the philtrum. Here's a Wikipedia image of this cleft in a dog:
It is a so-called vestigial structure of our anatomy, in the sense that Nature seems to have "left over" our philtrum as a useless relic of something that once existed—maybe as a functioning organ—in the bodies of our remote ancestors. It resembles—you might say—a mound of earth designating the former presence of an ancient castle, now gone. We humans retain a notorious vestigial creature that surely upsets naive folk who persist in believing that God created us in his divine workshop. I'm speaking of our tail bone. In my recent article entitled Ears, donkeys, a dog and birds [display], I spoke of the marvelous capacity of donkeys to orient their ears. In fact, we humans apparently possess vestigial traces of ear muscles. In other words, at one time or another in the very remote past, our ancestors were capable of hearing enemies creeping up on them from behind.
Concerning our curious philtrum, the following video demonstrates that it's simply the place where the two halves of our embryonic face are finally connected in a permanent fashion.
If a face were to be likened to a children's balloon, the philtrum might be thought of as the nozzle that you tie up with a piece of string, to keep the air in.
The philtrum is a bit like the navel of our head.