Limb bones form the framework of the human appendicular skeleton, providing structure and enabling movement. These bones serve as attachment points for muscles, allowing for a wide range of motion. They also protect soft tissues and contribute to the production of blood cells in their marrow.
Bones of the Upper Limbs
The human upper limb contains 30 bones, organized into the shoulder girdle, arm, forearm, and hand. The shoulder girdle connects the upper limb to the axial skeleton and consists of two bones: the clavicle and the scapula. The clavicle, or collarbone, is a long, slightly curved bone that attaches the arm to the chest. The scapula, or shoulder blade, is a flat, triangular bone serving as an attachment site for muscles.
The arm contains a single bone, the humerus, which extends from the shoulder to the elbow. The humerus articulates with the scapula at the glenohumeral joint, forming the shoulder joint. It connects with the forearm bones at the elbow joint.
The forearm, located between the elbow and wrist, contains two bones: the ulna and the radius. The ulna is positioned medially and plays a stabilizing role. The radius is located laterally and pivots around the ulna, allowing for movements like pronation and supination of the hand. The hand itself comprises 27 bones, including eight carpal bones in the wrist, five metacarpal bones forming the palm, and 14 phalanges making up the fingers and thumb.
Bones of the Lower Limbs
The lower limb also contains 30 bones, structured to support body weight, facilitate locomotion, and maintain balance. The pelvic girdle connects the lower limbs to the axial skeleton and consists of two hip bones and the sacrum. Each hip bone is formed by the fusion of three parts: the ilium, ischium, and pubis. It articulates with the head of the femur to form the hip joint.
The thigh contains the femur, the longest and strongest bone in the human body. Its rounded proximal end, the head of the femur, fits into the acetabulum of the hip bone. The patella, or kneecap, is a sesamoid bone located within a muscle tendon, articulating with the distal end of the femur to protect the knee joint.
The lower leg, situated between the knee and ankle, is composed of two bones: the tibia and the fibula. The tibia, also known as the shin bone, is the larger, medial bone and is the primary weight-bearing bone of the leg. The fibula is a slender, lateral bone that does not bear significant weight but provides muscle attachment and contributes to the ankle joint’s stability. The foot contains seven tarsal bones in the posterior portion, five metatarsal bones in the mid-foot, and 14 phalanges forming the toes.