The eight walking legs (also known as ambulatories) are numbered in pairs from the anterior (front) to the posterior (rear) of the crab. All of the legs have the same basic structure, although species-specific characters can vary across the legs.
Each limb is composed of seven segments (proximal to distal): coxa, basis, ischium, merus, carpus, manus, and dactyl. The first three (coxa, basis, and ischium) are small segments which attach the limb to the body of the crab. The merus is the first major segment, and the lagest on the limb.
The orientation of parts of the limbs and the segments of the limbs use the same terms as those used for the crab as the whole. The end of a segment closest to the body is the proximal end; the end of the segment farthest from the body is the distal end. The upper edge of the segment is the dorsal margin; the bottom edge is the ventral margin. The forward facing surface of the limb is the anterior surface; the rear facing surface is the posterior surface. Thus a reference to the proximal dorsal margin of the carpus would refer to the upper edge of the 5th segment (the 2nd major segment), near where the 4th and 5th segments join.