Brown adipose tissue is present in small mammals (e.g., mice) and in newborn humans. Most of it disappears in adult humans. The cells in both types of fat are called adipocytes although they differ in origin, structure, and function in the two types of tissue.
On the left hand, index finger. It's not the index finger you wear it on. Left hand, ring finger. The finger that you would wear a wedding ring on.
Logically it goes on your left hand- you are following tradition by getting married (albeit only recently for same sex couples) and it will indicate that you are married to everyone else. Any other finger and it is just a ring.