Connexus intertendinei

Tendons of the extensor digitorum muscle with the intertendine connexus

Connexus intertendinei are sinewy transverse bridges between the insertion tendons of the extensor digitorum muscle on the back of the hand. When you move your finger joints, you can sometimes see them under the skin and always feel them. These cross connections prevent the individual fingers from stretching in isolation. The index finger is least hindered and the ring finger is the most hindered. Practice (e.g. playing the piano) increases the freedom of the individual fingers, with the exception of the fourth finger.

The connexus intertendinei are a remnant of an originally broad connection of the extensor tendons that are still present in great apes. These are so strong there that only joint finger movements are possible. The restriction of this coupling is a sign of the advanced differentiation of fine motor skills in humans.

Cutting through the connexus intertendinei does not lead to better individual mobility of the fingers, since the extensor tendons are bound by the ligamentous apparatus of the joint.