Limb (anatomy) facts for kids

A limb (from Old English lim, meaning "body part") in anatomy is a jointed, muscled appendage of a tetrapod vertebrate animal used for weight-bearing, terrestrial locomotion, and physical interaction with other objects.

In human anatomy, the upper limb is divided into the arm, forearm, and hand, while the lower limb is divided into the thigh, leg, and foot. The human legs and feet are specialized for two-legged locomotion, while the arms are mobile and capable of grasping and fine manipulation of objects.

In most animals, the limbs are attached to the torso via girdles.

Types of limbs

There are various types of limbs in animals, which can be categorized based on their structure, function, and the number of limbs. Some of the different types of limbs include: Tetrapod limbs': These are limbs found in four-limbed vertebrates, such as humans, horses, and other mammals. They are organized into two bilaterally symmetrical pairs, with one pair at each end of the torso. The cranial pair (closer to the head) is known as the forelimbs or front legs, while the caudal pair (closer to the tail or coccyx) are the hindlimbs or back legs.

Arthropod legs: These are jointed and supported by hard external armor, found in insects and other arthropods. They are adapted for various purposes, such as walking, running, climbing, and jumping.

Bird limbs: Birds have two lower limbs, which are called legs. In place of upper limbs, they have two wings that help them fly. Birds also have a keeled sternum, which provides additional support for their flight muscles.

Prehensile limbs: Some animals, such as monkeys and some reptiles, have limbs that are adapted for grasping and manipulating objects. These limbs are called prehensile limbs and can be found in both front and hind limbs.

Fins: Some aquatic animals, such as amphibious fish, have fins instead of limbs. These fins are adapted for swimming and are part of their locomotory system.

Tail limbs: A few tetrapods, such as the macropods, have adapted their tails as additional locomotory appendages.

Development

Limb development is controlled by Hox genes. All jawed vertebrates surveyed so far organize their developing limb buds in a similar way. Growth occurs from proximal to distal part of the limb. On the distal end, the differentiation of skeletal elements occurs in an apical ectodermal ridge (AER) which expands in rays. A Zone of Polarizing Activity (ZPA) at the rear part of the AER coordinates the differentiation of digits.

See also

• Anatomical terms of location
• Anatomical terms of motion
• Ascending limb of loop of Henle
• Descending limb of loop of Henle
• Orthosis
• Phantom limb