Determination of Limb Polarities
The limb pattern is characterized by three axes (or polarities) as displayed in diagram:
(1) The direction from the shoulder (or hip) to the digits is the proximal-distal (P-D) axis.
(2) The cranial (head) side of the limb is anterior and the caudal (tail) side is posterior. The direction from the former to the latter side is anterior-posterior (A-D) axis.
(3) The third axis is the dorsal-ventral (D-V) axis which indicates the direction from the upper (dorsal) to the lower (ventral) side of the limb.
In your own hand the thumb is anterior and little finger posterior. The back of the hand marks the dorsal and palm the ventral side. You should also notice that the respective contralateral forelimbs and hindlimbs develop as mirror images of each other. For example, your right hand and foot are mirror images of the left hand and foot, respectively.