The curves in the human spine are characteristic, illustrating in another way the modification of the vertebral column that has been made necessary by the erect position. The new-born baby has a backbone that is almost straight, and in this respect it bears a strong resemblance to that of many of the lower animals. The typical human curves, however, begin to take form as soon as the child learns to sit up, and they become more marked as he learns to walk and run. These curves are essential to maintaining the balance of the body in the erect position. There are really three curves in the human backbone, the cervical curve being convex, the dorsal concave, and the lumbar convex, when each is regarded from the forward aspect. If we consider the sacrum and coccyx, there is really a fourth curve, this being concave, although in animals generally the coccyx curves backwards and is extended to form the tail. In some of the lower animals the spine is nearly straight, while in some cases it virtually forms a complete arch from one end to the other. These curves of the spine are generally more marked in the civilized white races than among the black and savage races, and as a rule they are more pronounced among women than among men. For instance, in comparing the sexes we find that in a woman the lumbar curve is more marked and extends slightly higher than in a man, and that the broad sacrum characteristic of the human race is even wider, being thus adapted to the broader hips and wider pelvic cavity of the child- bearing sex. Now, the maintenance of a strong and erect spine, and especially of the normal curves of youth is most important. With the weakness of advancing age the curves, particularly in the upper part of the spine, tend to become more pronounced. The more accentuated these curves are the greater is the weakness of the spine and of the muscles of the back that is indicated. It is said that a man is as old as his spine, since the deterioration of the spine means the loss of elasticity and supporting power in the disk-like cartilages between the vertebrae, and also the loss of strength in the muscles and ligaments of the back which tend to hold the spinal vertebrae in place. It is usually found that vigorous old men who are mentally and physically active at eighty or ninety years are those who have maintained an erect bearing until late in life, who have kept their spines straight and strong instead of allowing them to bend over and double up. In other words, the deterioration of the spine means a general loss of bodily vigor and a decline in the nervous energy or vitality.