A forelimb or front limb is one of the paired articulated appendages (limbs) attached on the cranial (anterior) end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used instead. In bipedal animals with an upright posture (e.g. humans and some primates), the term upper limb is often used. A forelimb is not to be confused with a forearm, which is a distal portion of the human upper limb between the elbow and the wrist. All vertebrate forelimbs are homologous, meaning that they all evolved from the same structures. For example, the flipper of a turtle or of a dolphin, the arm of a human, the foreleg of a horse, and the wings of both bats and birds are ultimately homologous, despite the large differences between them. Specific uses of the forelimbs may be analogous if they evolved from different sub-structures of the forelimb, such as the flippers of turtles and dolphins, and the wings of birds and bats. Evolution of forelimbs Evolution of the forelimb may be characterized by many trends. The number of digits, their characteristics, as well as the shape and alignment of radius, ulna, and humerus, have had major evolutionary implications. Changes in body size, foot posture, habitat, and substrate are frequently found to influence one another (and to connect to broader potential drivers, such as changing climate). Shape A number of factors can influence the evolution of forelimb long bone shape, such as body mass, lifestyle, predatory behavior, or relative prey size. A general pattern is for heavier species to have more robust radii, ulnas, and humeri. Musteloid carnivorans that have an arboreal lifestyle tend to have long and slender forelimb long bones, which allow for improved movement and flexibility. Semi-fossorial and aquatic musteloid species tend to have short and robust forelimb long bones to deal with the strain from digging and swimming. In the order Carnivora, felids, which usually ambush and grapple with their prey, have shorter and more robust limbs. Their forelimbs are used for both short sprints and grappling, which means that they need to be flexible and durable. In contrast, canids, which often pursue their prey over greater distances, have longer, more gracile limbs. Running is pretty much the only use for their forelimbs, so they don't need to be adapted for anything else and can be less flexible. Predators hunting prey