Unlike fingers, why are we unable to individually control our toes?
V.S. RAJASHEKHAR
Chennai
The difference between the movements of the hand and feet has anatomical and developmental reasons.
Anatomically, the muscles controlling the finger movements have separate bellies to individually move them. Especially the thumb and the little finger, each has 4 separate muscles in the hand called the thenar and hypothenar muscles respectively for finer movements. In contrast, the muscles of the toes except the great toe have a common bulk for their action. Hence when we try to move one toe, they move together. Also the structure of the joints and the attachments of muscles and tendons in the hand are such that the fingers can have a greater degree of mobility and independent movements compared to the toes.
Humans developed from four-legged apes. During this evolution, humans attained an erect posture with 2 legs and 2 hands. The primary function of the hand is to perform various skills and activities which are supported by the fine movements in the various joints and individual movements of the fingers. But the primary function of the foot is transmission of the body weight and for balancing during various activities. This function doesn’t require individual movements of toes.
Their weight bearing function is aided by the relatively stronger bones, rigid ligaments and fewer movements across joints. As humans started using the hands for various activities, the hand developed into an organ of more mobility and function. Thumb which constitutes about 40 per cent of the function of the hand is placed in a different plane to that of the other fingers and performs a wide range of movements. The movement of opposition by which the thumb can touch the tip of other fingers is a unique feature and improves the overall function of the hand. In contrast, the toes are located in the same plane with less degree of movements.
The hand movements have greater representation and control from the brain. The importance of hand is such that, the area of the brain allocated for hand function is higher than the area allotted for the entire lower limb.
Dr. SELVA SEETHARAMAN. S
Consultant Plastic Surgeon, Chennai
