Contribution à l’étude de la mobilité pollicale des primates actuels. Plaidoyer en faveur de l’importance du rôle de leur pouce
Fifty one anatomical specimens were dissected and the amplitudes of the trapeziometacarpal and metacacarpophalangeal joints of 33 were measured. These amplitudes were also measured on 26 animals asleep and many other animals were observed in relative freedom or in large aviaries. 419 skeletons of pr...
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| Format: | Article |
| Language: | English |
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Société Francophone de Primatologie
2013-05-01
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| Series: | Revue de Primatologie |
| Subjects: | |
| Online Access: | https://journals.openedition.org/primatologie/1217 |
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| Summary: | Fifty one anatomical specimens were dissected and the amplitudes of the trapeziometacarpal and metacacarpophalangeal joints of 33 were measured. These amplitudes were also measured on 26 animals asleep and many other animals were observed in relative freedom or in large aviaries. 419 skeletons of primates’ hands were measured and the measures converted in percentage with regard to the length of the 3rd metacarpal, in order to compare species in spite of their difference of size (collection of the Museum of Natural History in Paris). The morphological and functional differences of the trapeziometacarpal joint and the modes of pollicidigital prehension, help arranging primates in three categories.Among prosimians, the joint is concave/convex. The concavity follows a large vertical axis. Its articular surfaces are congruent. It works like a universal joint with two-degrees of freedom. Opposition with the two last fingers is only obtained with a maximum opening of the first commissure. Very long fingers are necessary to make a pinch. The 4th finger is the longest.Among platyrhinians, the joint is also concave/convex, but either slightly oblique or a little less congruent, or of condylar type (Callitrichinae). All fingers are long, especially the 3rd. The transversal intermetacarpal ligament of the first commissure hinders its opening. There is only pseudo-opposition in Cebidae and no opposition in Callitrichinae.In catarhinians, the joint has a 45 degrees tilt and its surfaces are not congruent. The attachment of the medial trapezométacarpal ligaments at the base of the metacarpal induces a rotation around its longitudinal axis. There are three degrees of freedom. Medial inclination is accompanied by pronation, which may be obtained with a very small displacement of the thumb. All the fingers are shorter than those of prosimians or platyrhinians. The thumb is particularly short. Only Macacus has a thumb almost as long as that of man. Two (sub-) families fall outside the rule. the Atelinae among the platyrhinians and the Colobinae among the catarhinians. Their first ray is atrophic and motionless; the thumb is almost buried in the thenar eminence.The metacarpophalangeal joint is condylar and unstable in almost all primates. This instability prohibits a powerfull and accurate grip. Only the human has a stable metacarpophalangeal joint. This stability is a critical factor during handling. The thumb is relatively long for a catarhinian. All these data on the pollical mobility are useful to understand the handling and the locomotion of the primates. These observations should help finding primitive characters of the hand of primates and to reconstitute a part of the evolution of the thumb toward its liberation. |
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| ISSN: | 2077-3757 |