🕷️ Each of a spider’s eight legs is made up of seven distinct parts. The part closest to the body, which attaches the leg to the cephalothorax, is the coxa; next is the short trochanter, functioning as a hinge for the long segment called the femur; then comes the spider's knee, the patella, which acts as a hinge for the tibia; followed by the metatarsus, which connects the tibia to the tarsus (often considered a foot); the tarsus ends in a claw made up of two or three points, depending on the spider's family. While most arthropods use muscles attached inside their exoskeletons to flex their limbs, spiders and some other groups still use hydraulic pressure to extend them—a system inherited from their pre-arthropod ancestors.⁠ ⁠ ⁠ ⁠ ⁠ #spiders #biology #biological #evolutionary #science #anatomy