NUMERICAL VARIATION IN THE HUMAN SPINE. 241 



be a change in development, distinctly strengthens the theory. This tendency makes for 

 the good of the organism as a whole, which is something more than an agglomeration of 

 fortuitous parts. Without this unifying principle the harmonious development of the 

 vai'ious parts is incomprehensible. An essential part of the office of the spine is to 

 form the median support of the trunk. The part above the pelvis may be considered as 

 an apparatus with sevei'al functions. It is therefore to be taken as a whole; and the 

 vertebra having most to do with its support can well be held homologous to the vertebra 

 doing, the same in other spines. If we admit this vitalistic conception, we can understand 

 that there is a tendency for parts in corresponding situations to develop in a correspond- 

 ing manner. Thus the penultimate lumbar vertebra (the 23d) has certain character- 

 istics which may be found when it is the 24th.* Rosenberg fully recognizes this fact, but 

 I do not see that he offers any explanation of its occurrence. The action of the vital 

 principle is also shown in moulding parts to aj^proach their normal conditions when some 

 disturbing cause has interfered with the usual course of development. Instances of this 

 will be given in the discussion of the spines. 



The next question to be settled is lohether there be a i^recise nmnber of human 

 vertebrae. It certainly is very unlikely. Fol has shown ('85) , and his discovery has 

 been confirmed, that at a very early time the human foetus has 38 vertebrae, some of 

 which, however, do not persist. It would require a much larger number of observations 

 than is likely to be made to convince one that the number 38 is absolutely constant, or 

 that even if it be, the same number always come to maturity. In point of fact there 

 seem to be no precise data. Steinbach ('89) found that the usual number of coccygeal 

 vertebrae in the male is five, and in the female four or five. For my part I have seen so 

 many cases in which I was unable to say with certainty whether or not certain nodules at 

 the end of the coccyx represented vertebrae, or certain constrictions a division between 

 two, that I admit my inability to count the coccygeal vertebrae in at least many cases. 

 According to all analogy it is very unlikely that there should be even a fairly definite 

 number. It is well known that variations in number of the vertebi-ae of the different 

 regions increase tailwards. All the spine below the vertebrae supporting the ilium, has 

 but a very subordinate function, and consequently is in an unstable condition. The 

 importance of this question is on account of the objection to the theory of inter- or 

 ex-calation or irregular segmentation, that it cannot be proved that certain elements nor- 

 mally on one side of the sacrum have not changed their position. This is true enough ; 

 but when the vertebrae at the borders of certain regions are characteristic ones and yet 

 there is an abnormal number between them, the objection does not seem weighty. 



' Rosenberg states that he has not himself found this condition in the case of 23 praesacrals nor, witli perhaps the excep- 

 tion of an observation by Tenchini, found an account of it by others. There is more than one instance of at least a near 

 approach to it in this series. 



