Hindlimbs

Hindlimbs are the rear pair of limbs in most vertebrates. They provide support, balance and propulsion during locomotion and can be modified for different ecological roles across species.

Anatomy: In humans the hindlimb includes the thigh (femur and patella), the leg (tibia and fibula), and the foot (tarsals, metatarsals, and phalanges). The hip, knee and ankle joints connect these segments. Major muscle groups include the gluteals and hip extensors in the thigh, the quadriceps at the front of the thigh, the hamstrings at the back, and the gastrocnemius and soleus in the calf. The sciatic nerve and its tibial and common fibular branches supply motor and sensory innervation; arterial supply comes from branches of the femoral and popliteal arteries.

Function and locomotion: Hindlimbs bear body weight, absorb impact, and generate propulsion. Gait patterns vary widely; in humans they support upright walking and running, whereas in many quadrupeds the hindlimbs provide the main drive during locomotion. Limb posture varies among species: plantigrade (whole sole on the ground), digitigrade (toes only), and unguligrade (hoofs).

Evolution and variation: Hindlimbs show diverse adaptations reflecting ecological roles, from grasping in some primates to running in cheetahs and hopping in kangaroos. In cetaceans hindlimbs are vestigial or absent, with pelvic bones present as internal remnants. Fossil forms illustrate the terrestrial transition of early tetrapods from fleshy-limb ancestry.

Development and clinical relevance: Hindlimbs develop from limb buds during embryogenesis under genetic regulation of limb-patterning genes. Clinically, hindlimb injuries include fractures of the femur or tibia, knee injuries such as ligament tears, and neuropathies affecting leg function. In veterinary medicine, hindlimb lameness is a common concern in dogs and horses.