226 / THE ERECT POSITION IN MAN. 



curvature at the base of the skull. In the monkey's neck 

 the convexity of the curve is forwards (downwards), in the 

 dorsal region and loins a continuous curve backwards (up- 

 wards), whilst the sacrum is feebly curved, and the coccyx 

 greatly. The non-possession of a separate lumbar curve by 

 animals is a very remarkable fact ; in the proper monkeys no 

 such curve exists. Lateral curves are feebly marked in the 

 animal spine. 



cl. In no animal does the sacrum develope so much in the 

 transverse direction, nor present so large an area of articula- 

 tion for the haunch, nor become so much curved as in man. 



e. The centres of gravity of the human trunk and body, 

 respectively, in their normal erect positions, are situated, the 

 former in the ninth dorsal vertebra, the latter in the interior 

 of the canal of the second sacral vertebra. By the term body 

 is meant the entire frame, trunk, and limbs. Movements of 

 the heart, changes in the circulation of the blood, in the 

 liver, etc., slightly affect the position of the centre of gravity. 

 In no animal can the centre of gravity be in these positions — 

 it must be situated below the vertebral column. 



/. In none of the mammalia do the articular facets of the 

 vertebral column possess such surface curvatures as to admit, 

 throughout its pre-sacral portion, that amount of torsion 

 possessed by the ascending portion of the human spine. 



g. No mammal possesses vertebral and trunk muscles so 

 fully differentiated, and so spirally arranged as in man. The 

 muscles of the trunk, obliqui, serrati, etc., are arranged in con- 

 tinuous corkscrew-like spirals around the body, as was first 

 pointed out by E. Weber. The peculiar spiral attitudes into 

 which the human body can be thrown are explained by the 

 spiral curve of the vertebral articular surfaces, and the spiral 

 arrangement of the muscles. 



h. No mammal can throw its trunk into those spiral 

 curves which subserve the balance of the human frame, and 



