Limb (anatomy)
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A limb (from
touching and striking
.
All tetrapods have four limbs that are organized into two
fly. Aquatic and semiaquatic tetrapods usually have limb features (such as webbings) adapted to better provide propulsion in water, while marine mammals and sea turtles have convergently evolved flattened, paddle-like limbs known as flippers
.
In
walk and run on all four limbs, human limbs are proportionally weaker but very mobile and versatile, and the unique dexterity of the human upper extremities allows them to make sophisticated tools and machines that compensate for the lack of physical strength and endurance.[2]
Anatomy
Limbs are attached to the
pelvic girdle for the hindlimbs. In terrestrial tetrapods, the pectoral girdles are more mobile, floating over the rib cage connected only via the clavicles (to the sternum) and numerous muscles; while the pelvic girdles are typically fused together anteriorly via a fibrocartilaginous joint and posteriorly with the vertebral column (sacrum), forming an immobile ring-like pelvis. The girdles are each connected to the corresponding limb proper via a ball-and-socket synovial joint
.
The overall patterns of forelimbs and hindlimbs are
pentadactyly) that they are given shared terminologies for each component of the appendicular skeleton.[3]
- The (proximal hindlimbs).
- The of the shin.
- The distalmost portion or extremity of the limb, i.e. the hand or foot, is known as the autopodium (plural: autopodia). Hands are technically known as the manus, and feet as the pes.
- The proximal part of the autopodium, i.e. the wrist or ankle region, has many small nodular bones, collectively termed the mesopodium (plural: mesopodia). Wrist bones are known as the carpals, and ankle bones are known as the tarsals.
- The middle part of the autopodium is the metapodium (plural: metapodia), composed of the slender long bones each called a or planta.
- The distalmost part of the autopodium are the phalanges and are highly mobile in most tetrapods. The ends of the digits are often protectively covered by hardened keratin outgrowths such as claws and nails.
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.[3]
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
References
| Fins |  | |
|---|---|---|
| Limbs |
| |
| Wings | ||
| Evolution | ||
| Related | ||
