THE ASCENT OF MAN. 457 



elastic strap — the ligamcntHm nuchoc — passing from the tips of the 

 thoracic vertebrte to the occiput, sending processes to all the neck ver- 

 tebne involved in the strain. Though need for it has in great degree 

 ceased since the head has become poised in such a way as to involve 

 but little expenditure of muscular force, yet relics of this great suspen- 

 sory apparatus remain in man's neck in the form of thickened fascial 

 bands. 



The arrangement of the great foramen of the slcull that transmits 

 the central axis of the uervous system, the si)inal cord, is necessarily 

 different in an animal carrying its head erect. The foramen would 

 naturally tend to be set forward more under the center of gravity and 

 its inclination would be more nearly horizontal. Here again mc see 

 that the ideally perfect form is more nearly approached in the civilized 

 races. It is never quite realized, and indeed the whole skull and its 

 contents evince markedly that they are still undergoing an evolution. 

 Again the lower races show variations that unite them with the anthro- 

 poid apes. While a negro may have a foramen magnum inclined 37 

 degrees to the horizontal, the orang may fall to .30 degrees. 



But it is not only in this way that we get evidence that the erect 

 position has been gradually acquired. Since gravity plays an impor- 

 tant part in the functions of the visceral and circulatory systems, any 

 marked change in the line of equilibrium must necessarily be accom- 

 panied by disturbances. These disturbances to a certain extent con- 

 iiict with the acquirement of the position, as they weaken the animal. 

 In the course of time tiie body may perhaps become adapted to the 

 changed conditions, but before that perfect adaptation takes place there. 

 is a iieriod of struggle. There is abundant evidence that such a strug- 

 gle has occurred and is yet going on, the adaptation being as yet far 

 from complete. 



The most striking and important of these adaptations concerns the 

 pelvis. When the erect posture is assumed the weight of the viscera 

 being thrown upon this bony girdle, it becomes adapted for their sup- 

 port by assuming a more fixed and dish-like shape. This is naturally 

 more pronounced in the female, since with her the pelvis nnist bear 

 the additional weight of the pregnant uterus. It is evident that a 

 solid, unyielding, laterally expanded ring of small aperture would give 

 the most effective support in the erect position, but it is equally clear 

 that with any such structure parturition would be impossible. In the 

 quadruped the act of parturition is comparatively easy, thepelvuj offer- 

 ing no serious hindrance. The shape of the female pelvis is therefore 

 the result of a compromise between two forms, one for snpiK)rt, the 

 other for ease in delivery. When we reflect that along with the 

 acquirement of the erect position, the size of the head of the child has 

 gradually increased, thus forming still another obstacle to delivery an<l 

 to the adaptation which might otherwise have taken placic, we can 

 realize how serious the struggle has been, and no longer wonder that 



