456 THE ASCENT OF MAN. 



center of gravity falling' behind the joint and the whole weight of the 

 trunk being hung upon the iliofemoral ligament, a heavily thickened 

 portion of the joint capsule. This structure is much more marked in 

 man than in other mammals, and is found to vary considerably in its 

 size and strength. 



The spinal column has been remarkably modified to adapt it to the 

 erect position, liefore the tifth month of uterine life the whole spine 

 describes a single, large, dorsally directed curve like that of the quad- 

 ruped, arranged to accommodate the viscera. As this would be inconi- 

 l)atible with the erect posture, two additional curves in the opposite 

 direction are formed : one in the region of the loins just where the center 

 of gravity would begin to fall forward, another in the neck to counteract 

 the heavy and unstable weight of the head. These curves are gradually 

 acquired. While possessed by all races, and in a less degree by the 

 higher apes, they arrive at their highest development in Europeans; 

 while the lumbar curve of the lower races of men is much better 

 adapted to running in a semi-erect position through the jungle or bush. 

 Careful measurements show that the shapes of the vertebme have been 

 gradually modified. There is no abrupt transition from the spine of the 

 lowest savages — Australian, Bushman. Andaman — to that of the gorilla, 

 gibbon, and chimpanzee. 



There is also evidence that the posterior limbs have moved forward 

 upon the spinal column in order that the erect position may be assumed 

 with less eftbrt. In man there are between the skull and the sacrum 

 twenty-four vertebra?. The other primates have usually twenty-six, 

 although the gorilla, chimpanzee, and orang agree with man. Now in 

 fcetal life the attachment of the hipbones to the sacrum commences 

 from below upward. Union first occurs with the third sacral vertebra, 

 leaving twenty-six pre sacral, then advances forward, the first sacral 

 uniting last of all. The hip-bones actually move up along the spine a 

 distance of two segments. Occasionally this shifting is carried still 

 further, and but twenty-three pre sacral vertebr;B are left. Anomalies 

 caused by an arrest of development at some stage of this process are 

 not at all infrequent. Tlie most common is the want of union between the 

 hip-bones and the first sacral vertebra, thus producing apparently six 

 lumbar vertebne. A most beautiful specimen of this anomaly was found 

 last winter in my laboratory. 



The si)ine is sustained erect by stringing from vertebra to vertebra 

 numbers of short ligaments that reduce to a minimum the muscular 

 exertion required to support it. These are particularly numerous be- 

 tween the spines along the great dorsal curvature. Some of these lig- 

 aments are replaced by small muscles, very inconstant and variable, 

 the survivals of a whole system of musculature that had for its object 

 the moving of the separate joints of the spine, one upon another. 



The head is also much modified by the erect i)osition. In quadru- 

 peds, its suspension requires an extensive apparatus, a large, stroug, 



