346 



dently of the other. As even then the rotary motion is probably less 

 than normal, the joint between the occiput and the atlas is less cup- 

 shaped and more adapted to a sliding motion than usual. It is interest- 

 ing to observe a very similar conformation in the sockets for the con- 

 dyles on the atlas of H-3, which is fused with the atlas. Thus rotary 

 motion is possible to some extent in that joint, and the work of flexion 

 and extension was no doubt in part carried on by the other joints of 

 the cervical vertebrae. To the action of the same cause we must 

 turn for the modification in the length of the thoracic vertebrae, by 

 which 11 more than compensated for the ordinary 12. In the same 

 way is to be explained the modifications of which we have had so 

 many examples, by which an approach to the normal dispositions of 

 regions is so often obtained. Still another instance is furnished by 

 spine 202, in which a cervical rib which ends free has a cartilage 

 shooting out from the manubrium to meet it. Similar cases have been 

 described by Leboucq and others. This shows clearly that the pro- 

 duction of the costal arch depends on something more than the over- 

 development of the costal element of the vertebra. It begins at both 

 ends in cases which approach a complete arch. Clearly there is some 

 force acting throughout the organism, not at one point alone, to in- 

 augurate such changes. 



If Rosenberg's views on the changes of position of the iliura^ 

 and the consequent modification of vertebrae according to the position 

 it finally assumes, which we have provisionally adopted, be correct^ 

 there is the evident need of some explanation of the cause of these 

 modifications. I can see no other than the action of the vital prin- 

 ciple. If it be objected that this is only a name to cover our ignor- 

 ance, then the objection must be made against gravitation, magnetism, 

 etc., for in no case do we know how the force works. We see only 

 results. 



Apart from other deductions, the following conclusions seem 

 justified. 



I. Variations occur in two ways: 1) by irregular development 

 of the costal elements at and near the ends of the regions of the 

 spine, and 2) by irregular segmentation through which there are more 

 or fewer vertebrae than normal. 



II. Variations of both kinds are variations around a mean. It 

 is not impossible that some of them may be reversive; that any are 

 progressive is mere assertion. 



III. Assuming the correctness of Rosenberg's studies in onto- 

 genesis, his view may account for some of the variations, but even 



