IT WAS an emergency. A young girl lay in the hospital entranceway, the main artery in her right leg having been severed in a motorcycle accident. No surgical instruments were on hand to stop the blood pumping out of the wound. What could the doctor do?

“I used my hand as a clamp,” recalls Professor Napier in his book Hands, “pinching off the artery with thumb and fore-finger as well as I could. Finally I got a bit of string, all that was available, round the artery and tied it off. The blood stopped pumping. . . . Nothing but the hands could have dealt with that emergency so quickly and effectively. Few patients . . . ever realise how, during an operation, an appropriately placed finger has saved their lives.”

Actions like these would be impossible were it not for the saddle joint of the thumb. (See illustration.) Its design allows almost as much movement as the ball-and-socket joint of the shoulder, but unlike the latter, the saddle joint does not need support from a surrounding mass of muscles. The thumb, therefore, can perform delicate movements as it meets the fingertips.

Try picking up a small object or even turning the pages of this magazine without using your thumb. Said a South African doctor: “I have put plenty of injured thumbs in splints, and when the patients come back, they usually tell me they didn’t realize how much they needed their thumb.”

The human hand with its opposable thumb is a remarkably versatile tool.

[Pictures on page 5]

The saddle joint of the thumb is unique when compared with the corresponding joints of the fingers