Structural Diversity of the Extensor Digitorum Profundus Muscle Complex in Platyrrhini

Separate extension of fingers in the hand of primates is performed by 3 muscles: m. extensor pollicis longus, m. extensor digiti secundi, and m. extensor digitorum lateralis. Here it is proposed to consider them as parts of the extensor digitorum profundus muscular complex. The diversity in structure of these muscles in primates is examined based both on original anatomical study of New World monkeys and analysis of extensive published data on primates from different taxonomic groups. It is shown that in these muscles there are 2 main types of structure variations - the division of the muscle belly into several heads which give rise to separate tendons, and the split of the single terminal tendon into several branches. The first type of modification ensures the possibility of a separate management of the fingers, and the second, on the contrary, ensures the coupled control of extension of fingers. A scheme of evolutionary transformations of muscles belonging to the complex of the deep extensors of fingers is proposed.