Comparative anatomy, homologies and evolution of the pectoral and forelimb musculature of tetrapods with special attention to extant limbed amphibians and reptiles

V. ABDALA; R. DIOGO

JOURNAL OF ANATOMY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Irlanda; Año: 2010 vol. 217 p. 536 - 573

0021-8782

The main aim of the present work is to synthesize the information obtained from our dissections of the pectoral and forelimb muscles of representative members of the major extant taxa of limbed amphibians and reptiles and from our review of the literature, in order to provide an account of the comparative anatomy, homologies and evolution of these muscles in the Tetrapoda. The pectoral and forelimb musculature of all these major taxa conform to a general pattern that seems to have been acquired very early in the evolutionary history of tetrapods. Although some muscles are missing in certain taxa, and a clear departure of this general pattern is obviously present in derived groups such as birds, the same overall configuration is easily distinguishable in these taxa. Among the most notable anatomical differences between the groups, one that seem to have relevant evolutionary and functional implications, concerns the distal insertion points of the forearm musculature. While non-mammalian tetrapods often have carpal bones such as the radiale as the most distal insertion point of the flexor radial complex of the forearm, in mammals the muscles of this complex often extend distally to insert onto hand bones (for instance, the flexor carpi radialis often inserts onto metacarpals I and/or II). Interestingly, a similar trend (towards a more distal insertion onto hand bones) is also found in some anurans with peculiarly subtle digital movement abilities, such as Phyllomedusa. One can thus argue that the complexity of the ‘extrinsic’ musculature of the hand (i.e., of the forearm musculature), as well as the more distal insertion of at least some of its components, evolved in a few, derived tetrapod taxa in correlation with the acquisition of these more subtle digital movement abilities.