Tony Heald / African elephant calf on knees by water {Loxodonta africana} Kaokoland, Namibia

Tony Phelps / Bontebok (Damaliscus pygargus pygargus) males down on their knees, sparring, DeHoop Nature reserve, Western Cape, South Africa, August

Charlie Summers / White-bearded Gnu / Wildebeest (Connochaetes taurinus) in a dominance fight on their knees with dust flying. Ngorongoro Crater, Tanzania.

Michel Poinsignon / Bald cypress knees (Taxodium distichum) Courant d'Huchet Landes, France, August.

Michel Poinsignon / Bald cypress knees (Taxodium distichum) Courant d'Huchet Landes, France, August.

Michel Poinsignon / Bald cypress tree (Taxodium distichum) and knees, Courant d'Huchet, Landes, France, August.

Michel Poinsignon / Bald cypress tree (Taxodium distichum) and knees next to river, Courant d'Huchet, Landes, France, August.

Petra Wegner / Woman sitting holding tissues s with Cavalier King Charles Spaniel, ruby, male with paws on her knees Model released

Jeff Rotman / El Molo child suffering from rickets, caused by a diet consisting primarily of fish. El Molo children suffer from vitamin D deficiency, which develops into the nutritional disease causing deformities...

Adrian Davies / Bald Cypress tree(Taxodium distichum) 'Knees' Corkscrew Swamp Sanctuary, Florida, USA, January.

LYNN M. STONE / Domestic goat (Capra hircus) Oberhasli breed male goat resting on knees while grazing, East Troy, Wisconsin, USA

LYNN M. STONE / Domestic goat (Capra hircus) Oberhasli breed male kneeling to graze, East Troy, Wisconsin USA

Chien Lee / Stick Insect (Carausius sanguineoligatus) male showing bright red knees, Mount Kinabalu National Park, Borneo, Malaysia

Bernard Castelein / Avocet (Recurvirostra avosetta) adult crouched down on its 'knees' to shelter chicks, Texel, the Netherlands

Bernard Castelein / Avocet (Recurvirostra avosetta) adult crouched down on its 'knees' to shelter chick, Texel, the Netherlands

Bernard Castelein / Avocet (Recurvirostra avosetta) adult crouched down on its 'knees' to shelter chicks, Texel, the Netherlands

John Cancalosi / Bald cypress tree (Taxodium distichum) knees (woody projections sent above the ground or water that are part of the root system) Louisiana, USA

Jane Burton / Bay mare and filly, filly bending her knees in order to reach down and sniff the grass, UK

Albert Lleal / Leopard Gecko (Eublepharis macularis) albino photographed under ultraviolet light, showing strong fluorescence at the knees, fingers, and in the face, native to Asia

Nigel Bean / Close up of legs of Grevy zebra {Equus grevyi} captive

Juergen Freund / Root knees and stumps of felled swamp Bald cypress trees (Taxodium distinchum), Florida Panhandle, USA

Juergen Freund / Stumps and root knees of swamp Bald cypress trees (Taxodium distinchum), Florida Panhandle, USA

David Shale / Mexican Red-Knee Tarantula spider {Brachypelma smithi} close-up of diagnostic red knee, Captive

Richard Du Toit / Female warthog on knees feeding (Phacochoerus aethiopicus} South Africa.

Nick Garbutt / Warthogs grazing on knees {Phacochoerus aethiopicus} Hwange NP Zimbabwe

Gerry Ellis / African Elephant (Loxodonta africana) orphan on knees in mud bath, David Sheldrick Wildlife Trust, Tsavo East National Park, Kenya

Adrian Davies / Bald cypress {Taxodium distichum} showing root knees, Big Cypress swamp Florida USA

Richard Du Toit / Yellow billed stork resting on 'knees' {Mycteria ibis} Chobe NP, Botswana