Carpus and tarsus of land vertebrates
Encyclopedia
Carpus
In tetrapods, the carpus is the sole cluster of bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do. The corresponding part of the foot is the tarsus...
(wrist
Wrist
In human anatomy, the wrist is variously defined as 1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand;...
) and tarsus
Tarsus (skeleton)
In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...
(ankle
Ankle
The ankle joint is formed where the foot and the leg meet. The ankle, or talocrural joint, is a synovial hinge joint that connects the distal ends of the tibia and fibula in the lower limb with the proximal end of the talus bone in the foot...
) of land vertebrates primitively had three rows of carpal or tarsal bones. Often some of these have become lost or fused in evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
.
- Three proximals. In the hand humans has all three. In the foot the middle proximal appears in 5-15% of people as an os trigonum.
- Centrale or os centrale, on the medial side. In humans and our closest relatives the African apes (chimpanzees and gorillas) it fuses to the scaphoid where it forms the articulation with the trapezoid bone; occasionally it stays separate. In Man's foot it is the navicular. Some early land vertebrates had more than one (up to three) os centrale per hand or foot (plural "(ossa) centralia").
- Distals, one per finger / toe at the base of each metacarpal or metatarsal. In mammalMammalMammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s the 4th and 5th fuse. In the horseHorseThe horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
the 1st is lost.