The Marvels of the Human Hand
By EVAN MCLEOD WYLIE
In the darkness of a mother’s womb a tiny, ivory-colored embryo enters its fourth week of life. Within the tightly curled, motionless organism, scarcely two inches long, millions of new cells are growing at an enormous rate. From the side of the reck region sprouts a pair of “buds”. Rapidly they elongate into three segments. The extreme outer segment assumes a paddle shape. Five lobes appear on the edges of the paddle. Muscles, tendons and nerve fibers develop. By the third month of pregnancy, the little flipper’s miniature fingers flex spasmodically. A human hand has been formed.
Months later, when the baby is delivered, these little fingers will clutch and pluck at the hands of the obstetrician with startling insistence. From then on, the hands of this human being, directed by the brain, will chiefly determine how this life differs from the lives of all other creatures on earth.
No other part of the body is so intimately associated with human behavior. With our hands we work, play, love, heal, learn, communicate, express our feelings, construct our civilizations and create our works of art. The hand and our emotions are so linked that, for most of the world’s peoples, clasped hands symbolize faith, love and friendship, while the clenched fist is the unmistakable expression of human strength and resolution.
How and when during the immense span of evolutionary time did this extraordinary appendage originate?
Amazingly, the fin of the fish is the forerunner of the human hand. As fish crept out of the sea and developed into air breathing amphibians, their fore fins developed into instruments for crawling, gripping, creeping; and through millions of years subsequent evolution their basic four-limbed artichetecture persisted. Watch goldfish in an aquarium. The delicate motion of the fins just behind its head as they fan the water to regulate its movements is controlled by a set of muscles, which are the rudiments of our intrinsic hand muscles.
Once of the most complex instruments of the entire body, the hand is an intricately engineered mechanical device composed of muscle, fat, ligament, tendon, bone and highly sensitive nerve fibers. It is capable of performing thousands of jobs with precision. To make the simplest grasping motion, and array of muscles, joints and tendons all the way from shoulder to fingertips is brought into play. Taking a spoonful of soup involves more than 30 joints and 50 muscles.
The hand is packed full of bones, eight in the wrist, five in the palm, and 14 in the fingers of one hand. The ligaments, cords of stringy material, hold all these bones together at the joints. The tendons, tough fibers that guide hand and wrist bones and link them to the muscles that operate them, control finger motion.
The thumb, operating independently of the other four fingers, is the busiest and most important of all the drifts. Because of the thumb’s unique ability to cross over and link up with any one of the other fingers, we can get along with one thumb and one other finger, or even the stump of a finger.
The rest of the fingers are markedly different in strength. The middle finger is usually the strongest, followed by the index finger; the fourth finger is considered by the teachers of music and typewriting to be the less least responsive to training because of an innate muscular weakness; the little finger is weakest of all.
The size of a person’s hand is not significantly related to the strength of its grip or whether it will be fast or slow, deft of clumps. Among musicians, physicians, artists, athletes and others who depend on their hands to earn living, there is an infinitive variety of stubby fingers, slender fingers, large hands and small hands.
Human fingers can be trained to perform astonishing feats. The flying fingers of a master pianist can strike 120 notes per second. With two fingers, a skilled surgeon can tie strands of thread into tight knots inside the human heart. A circus performer so strengthened the index finger of his right hand by years of patient effort that he can balance himself on its tip.
Every walking moment we obtain a great deal of information about the things we touch by the “feel” of them. This is possible because the skin of the hand is not like the skin of an other part of the body. While extraordinary tough, it is also wonderfully elastic and incredibly sensitive.
The skin of the back of your hand actually stretches by almost half an inch when you grip or squeeze something; simultaneously, the palm inside is shortened by half and inch. Beneath the thick skin of the palm is a buffer of fat which protects the vital tendons and blood vessels of the hand while the outer surface is being subjected to the tremendous friction created by scraping, twisting, gripping and clenching motions.
The palm of the hands, and particularly the fingertips, are equipped with special sensory apparatus. A piece of finger skin smaller than a postage stamp contains several million nerve cells. Of the surface of the skin are ridges formed by papillae. These are dotted with myriad pores and nerve endings, which detect the temperature and texture of anything we touch. [Fingerprint identification is based on the fact that the whorl patterns created by these papillae are never identical in two people]
The greatest natural enemy of the human hand is cold, because bloodless joints in which the temperature drops more quickly than it does in blood filled muscles take up most of the finger. That is why you can skate of ski all day in zero temperature without covering your face, which is full of muscles richly supplied by warm blood, while without gloves your fingers grow painfully numb in minutes. Finger joints, like all other body joints, are bathed in a colorless, viscous lubricating fluid [synovia], which provides a smooth, gliding action when we bend an elbow or a finger. When this fluid gets cold, it thickens and finger joints stiffen.
Because of its intricate arrangement of nerves and muscles, the hand is highly vulnerable to injury. Injuries to wrist, fingers and hands account for almost one half of the total casualties in industrial accidents. All lacerations of the hand are potentially dangerous because holders of virulent organisms swam over the things we touch daily. The thick skin of the hand provides an impregnable barrier to these bacteria. But if a scratch of puncture permits then to gain entrance, infection may follow swiftly.
Our hands deserve careful treatment. As tools of learning, working and communicating, they can be considered the fundamental vehicle of human thought—partner with the brain in forever separating man from the rest of the animal kingdom.