SUPPORT AND MOVEMENT 



379 



about them is that the patients often re- 

 covered, as revealed by the smooth edges 

 of the opening, indicating that the bone 

 healed. Similar operations are performed 

 today for entirely different reasons and 

 with much more satisfactory results. 



The spinal column. When a comparison is 

 made between the spinal column of man 

 and almost any of the other mammals, cer- 

 tain striking differences are noted (Fig. 

 15-4). These result from the upright pos- 

 ture man has assumed. In the dog, for 

 example, the column forms a smooth arch 

 between the two pairs of legs; in man, on 

 the other hand, it forms a sigmoid or 

 S-shaped curve. This serves an important 

 purpose in an upright animal. With the 

 head resting on the top end of the column, 

 a rigid, straight rod would afford very little 

 resilience whereas a curved column would 

 spring gently, thus cushioning the jolts that 

 are conducted through the legs from the 

 feet as they come in contact with the 

 ground. The curved spine of man is ad- 

 mirably designed to give the head a smooth 

 ride. If the pliable spine of a growing child 

 is subject to undue stress, it may ultimately 

 affect the development of the adult skele- 

 ton. Much of our posture is dependent on 

 the spine and there is much emphasis to- 

 day on the desirability of good posture. 

 While this is highly desirable, it is not a 

 guarantee of good health. Good health 

 is due to a great many things and cannot be 

 guaranteed by any such simple formula. 



The spinal column is composed of 33 

 articulating vertebrae of rather irregular 

 sizes from the neck to the pelvis and they 

 fit snugly together. They are securely laced 

 together by many ligaments, so that the 

 column as a whole is a beautiful piece of 

 engineering. This is essential because the 

 column houses the very delicate spinal cord 

 which, if injured even only slightly, may 

 cause dire effects in the operation of the 

 appendages as well as other parts of the 

 body. The column is more flexible in some 

 regions than in others. For example, the 



Fig. 15-4. The spinal column is the axial support of 

 vertebrates and is subject to considerable variation 

 among the different groups, depending on the stress 

 and strain put upon it. In the quadraped, such as 

 the dog, the column functions like a bridge v^rith the 

 two supports at either end. When the support is 

 shifted to the two posterior appendages, such as in 

 the ape, a more secure attachment must be affected 

 between the column and the pelvic girdle. This is car- 

 ried further in man, where we see a huge pelvic 

 girdle, since the posterior appendages must provide 

 the only means of support and locomotion. 



