NUMERICAL VARIATION IN THE HUMAN SPINE. 307 



there is an intercalation of the 3d vertebra, which, at least in one case, he considers a 

 partial reduplication of the atlas. In neither of my cases is there any reason to see more 

 than fusion. Leboucq asks whether we are to consider his finding twice an intercalated 

 vertebra at this place anything more than a simple coincidence. He think.s that the 

 place l^elow the axis is a critical one in the cervical column, and that the 3d vertebra is 

 exposed to more variations than the others. He cites Murie to the effect that the 

 reduction of the cervical vertebrae to six in the manatus arises from an almost complete 

 regression of the 3d. Putting aside the question of intercalation, the idea that this is a 

 critical point receives additional confirmation from the four cases in this series. 



Irregular Segmentation. — As was remarked earlier, this is much the same as inter- 

 and excalation, but preferable ; inasmuch as the latter terms too often are used to refer to 

 a particular vertebra supposed to be added or suppressed. There are cases in this series 

 both of tlie addition and of the want of a vertebra above the sacrum, in which the regions 

 are well defined and otherwise practically normal. Two striking examples are 764 and 

 478. The formula of the former is C. 7, T. 13, L. 5, S. 5, C. probably 5 ; that of the 

 latter is C. 7, T. 11, L. 5, S. and C. 9. In both, the cervical, lumbar and sacral regions are 

 very neai'ly typical. The fact that the 1st coccygeal is fused with the sacrum in both is 

 interesting as showing that it is prol)al)ly quite an indifferent occurrence. There eeems 

 to l)e no other way of accounting for these spines, and for others nearly as good, but by 

 admitting a departure from the usual segmentation. 



Concomitant Variations. — Ha\'ing discussed most of the variations, considered 

 separately, we have now to consider the relation of a variation at one part of a column to 

 a variation at another part. Allusion, indeed, has been made to the effect of a variation 

 in one vertebra on those in the immediate neighborhood, but now we are to consider 

 distant ones. 



This brmgs us to the central point in the discussion of Rosenberg's theory. It has 

 been remarked that he has admitted that it would be natural to expect some relation 

 between the condition of the spine at one end of the thoi-ax and that at the other, but 

 that such a relation is not to be found. Thus if the undeveloped condition of the 1st 

 thoracic rib is a step towards the future, it would be reasonable to expect in the same 

 spine a corresponding advance below the tliorax. Conversely, if there is an archaic condi- 

 tion below the thorax there should be an analagous condition above it. While there are 

 cases that fulfil these conditions, they are quite lost in the multitude which do not, and 

 which even present contradictory conditions at the opposite ends of the spine, being retro- 

 gressive at one end and progressive at the other. 



Let us take first the ten complete spines of this series with cervical ribs (including 



