FUNCTIONAL MORPHOLOGY OF THE FOREARM MUSCLES IN THE BROWN BEAR (URSUS ARCTOS): ADAPTATIONS TO PLANTIGRADE LOCOMOTION

Creative Commons License

Cherșunaru A., Teodor H., Spataru C., Szara T., Melnyk O., Gündemir O., ...Daha Fazla

REVISTA ROMANA DE MEDICINA VETERINARA, cilt.36, sa.3, ss.119-126, 2026 (ESCI)

Özet

The forearm of the brown bear (Ursus arctos, Ursidae, Carnivora) serves as a useful anatomical model for studying muscular adaptations in a large plantigrade carnivore whose behavior combines terrestrial locomotion, grasping, digging, and, in young individuals, limited climbing. This paper systematically describes the musculature of the forearm in Ursus arctos based on macroscopic dissection, with an emphasis on the morphology, architecture, and functional role of the main groups of muscles: digital and carpal flexors, digital and carpal extensors, pronators, and supinators. The results spotlight a deep flexor muscle (m. flexor digitorum profundus) with a pinnate appearance, involved in the powerful flexion of the claws, essential for digging or handling prey. The superficial flexor muscle (m. flexor digitorum superficialis) has a bipartite configuration, with a superficial pentadigital portion and a deep portion selectively inserted on the central fingers II–IV. The carpal flexors (m. flexor carpi radialis and m. flexor carpi ulnaris) contribute to the dynamic stabilization of the carpal joint under conditions of asymmetric mechanical stress, while the well-developed accessory carpal bone (Os carpi accesorium) amplifies the lever arm of the flexor carpi ulnaris muscle. The extensor group of muscles, comprising the digital and carpal extensor muscles (m. extensor digitorum communis, m. extensor digitorum lateralis, m. extensor carpi radialis, m. extensor carpi ulnaris), predominates on the craniolateral aspect of the antebrachium. These muscles play a critical role in stabilizing the forelimb during the stance phase of locomotion and facilitate active extension of the digits following forceful flexion. The pronator teres and pronator quadratus muscles are solely responsible for pronation, while the supinator muscles (m. supinator, m. biceps brachii) provide the forearm rotation necessary for grasping and, in juveniles, for climbing. Overall, the forearm musculature of Ursus arctos represents an evolutionary compromise between the retained arboreal capabilities characteristic of the Ursidae and the functional demands for strength, stability, and mechanical endurance associated with a large plantigrade carnivore exhibiting diverse locomotor and feeding behaviors. The findings presented here provide not only a detailed anatomical description of the zeugopodial musculature but also an integrated functional interpretation, demonstrating how muscular morphology reflects the ecological adaptations and behavioral repertoire of the species.