# Intermembral index

The intermembral index is a ratio used to compare limb proportions, expressed as a percentage. It is equal to the length of forelimbs (humerus plus radius) divided by the length of the hind limbs (femur plus tibia) multiplied by 100, otherwise written mathematically as:
${\tfrac {(humerus+radius)}{(femur+tibia)}}\times 100$
The intermembral index is used frequently in primatology, since it helps predict primate locomotor patterns. For scores lower than 100, the forelimbs are shorter than the hind limbs, which is common in leaping primates and bipedal hominids. Quadrupedal primates tend to have scores around 100, while brachiating primates have scores significantly higher than 100. This information can also be used to predict locomotion patterns for extinct primates in cases where forelimb and hind limb fossils have been found.

## Primate species

Intermembral Index of Extant Primate Species :
| Species | Intermembral Index |
| Cheirogaleus major | 72 |
| Microcebus murinus | 72 |
| Phaner furcifer | 68 |
| Lemur catta | 70 |
| Hapalemur griseus | 64 |
| Eulemur fulvus | 72 |
| Lepilemur edwardsi | 60 |
| Avahi laniger | 58 |
| Indri indri | 64 |
| Daubentonia madagascariensis | 71 |
| Galagoides demidovii | 71 |
| Galago senegalensis | 52 |
| Otolemur crassicaudatus | 70 |
| Perodicticus potto | 88 |
| Arctocebus calabarensis | 89 |
| Loris tardigradus | 90 |
| Nycticebus coucang | 88 |
| Carlito syrichta | 58 |
| Cephalopachus bancanus | 52 |
| Callicebus moloch | 74 |
| Pithecia pithecia | 75 |
| Chiropotes sagulatus | 83 |
| Cacajao calvus | 83 |
| Alouatta seniculus | 97 |
| Lagothrix lagotricha | 98 |
| Brachyteles arachnoides | 104 |
| Ateles paniscus | 105 |
| Cebus capucinus | 81 |
| Sapajus apella | 81 |
| Saimiri sciurius | 80 |
| Aotus lemurinus | 74 |
| Callimico goeldii | 69 |
| Callithrix jacchus | 76 |
| Cebuella pygmaea | 83 |
| Saguinus geoffroyi | 76 |
| Leontopithecus rosalia | 89 |
| Macaca fascicularis | 93 |
| Macaca nemestrina | 98 |
| Cercocebus agilis | 84 |
| Mandrillus sphinx | 95 |
| Lophocebus albigena | 78 |
| Papio anubis | 97 |
| Theropithecus gelada | 100 |
| Mioithecus talapoin | 83 |
| Chlorocebus aethiops | 83 |
| Erythrocebus patas | 92 |
| Allochrocebus lhoesti | 80 |
| Cercopithecus mitis | 82 |
| Colobus guereza | 79 |
| Piliocolobus badius | 87 |
| Procolobus verus | 80 |
| Presbytis siamensis | 78 |
| Trachypithecus obscurus | 83 |
| Semnopithecus entellus | 83 |
| Nasalis larvatus | 94 |
| Pygathrix nemaeus | 94 |
| Hylobates lar | 130 |
| Symphalangus syndactylus | 147 |
| Nomascus concolor | 140 |
| Hoolock hoolock | 129 |
| Pongo pygmaeus | 139 |
| Pan troglodytes | 106 |
| Pan paniscus | 102 |
| Gorilla gorilla | 116 |
| Homo sapiens | 72 |

## Variation

In a diverse ethnic sample of 314 modern human skeletons covering African Pygmies, Andaman Islanders, Khoesan, Zulu, African Americans, Sami and Inuit the intermembral index was found to vary between 64 and 74. A study published in 1937 found a range of variation between 64.5 and 79.2. This study found no link with humans of different groups with individuals from different ethnic groups showing similar scatter of variation. Variation has also beem found in chimapanzees (100.1 - 113.7), gorillas (110.3 - 125.0), orangutan (135.0 -150.9), siamang (145.0 - 155.2), gibbon (120.5 - 137.1), and macque monkeys (83.0 - 91.0).