Thermography pictures for the human hand usually demonstrate that body temperature in the fingers is highest in the thumb and lowest in the pinky.
Finger proportions likely explain this temperature distribution, because thermography pictures for the full body show that the highest temperatures inside the full body are usually found at the core of the body - close to the spine which is located at the central axis of the torso (see picture on the right).
The parallel between the body temperature distribution inside the hand and the body is an illustration of the anatomic fact that body parts and bones tend to become more narrow and thinner at the extremities of the body.
Western hand reflexology charts usually present a map for the human body (in terms of body parts and internal organs), where the thumb gets associates with the internal spine and the pinky finger gets associated with the body extremities (= arms & legs) plus other externalized body parts (such as the ears).
Other body parts & organs are mapped between the thumb and the pinky.
The maps below describe some details as described in the interactive hand reflexology chart presented by Kevin & Barbara Kunz.
Hand temperature distribution: thumbs have the highest temperature.