104 ARBOREAL MAN 



underlying cause of the variations. Some fift}' j^ears ago 

 Paul Topinard dealt partially with this problem, which 

 had previously engaged the attention of Paul Broca. 

 But these two authors considered little more than the 

 end of the story, for they took most note of those changes 

 which have taken place in so short a chapter as that 

 comprised in the study of the higher Primates and Man. 

 It is, however, necessarv to embrace far more than this 

 in the study of what Topinard termed " anteversion and 

 retroversion " of the spinous processes. If we take the 

 skeleton of such a well-known animal as the dog it is at 

 once apparent that the spines of the cervical and most 

 of the dorsal vertebrae are " retroverted," that the 

 penultimate dorsal vertebra is " anticlinal," and the two 

 last dorsal and all the lumbar vertebrae have spines that 

 are " anteverted," another upright spinous process ap- 

 pearing on the sacrum. The anticlinal vertebra which 

 is situated, in the dog, near the end of the dorsal, or rib- 

 bearing, series has also been termed the region of the 

 " centre of motion " ; and it is easy to realize, in watching 

 a greyhound looping along, that this is a perfectly well 

 justified term. The anticlinal vertebra indicates that 

 the animal possessing it has the power of bending its 

 vertebral column as a spring is bent, and that the apex 

 of the bend is situated at this particular point. The 

 presence of such a vertebra in the backbone, whether 

 of a recent animal or a fossil, shows clearly that the 

 animal could flex and extend its vertebral column about 

 this central point, and that its spine could be bent, and 

 could be straightened out again as a spring in the ordinary 

 activities of the animal (see Fig. 36). Tliese things are 

 clear enough when we look at the skeleton of a dog, or a 

 hare, and weave into the bones the picture of the animal 

 laying itself out, and doubling itself up, as it goes at full 

 speed. But there is, as we have seen, another condition 

 — that seen in some primitive Reptiles and Mammals — 

 in which the anticlinal vertebra is situated, not in the 



