4 testicles??

Question
I have a 6-8 month old chocolate lab and I have noticed that he has the normal Scrotum and testicles but at the base of his "thing" he has what looks to be another pair of testicles... or is this something else? when he gets "excited" they enlarge and when he's relaxed they reduce in size to where you almost cannot notice it. My question is, Is it possible to be another set of testicles or is this just a natural thing in labs?  

Answer
What you are seeing is the "bulbis glandis" not 2 more testicles.  

It has nothing to do with Labs, it's a "dog thing".  You can google the term I gave you, but it's basically the part of the dog penis that allows the male to tie with the female during breeding.