VARIABILITY IN THE SPINAL COLUMN AS REGARDS 



DEFECTIVE NEURAL ARCHES 

 (RUDIMENTARY SPINA BIFIDA). 



BY THEODORA WHEELER. 



Studies of minor variations are continually being presented in biological fields. 

 The reason for the persistent attention directed toward this line of study is not far 

 to seek. To any observer the more or less frequent appearance of varied charac- 

 teristics in form or function can not fail to suggest many perplexing questions as to 

 the causes underlying such processes, and also as to their immediate and ultimate 

 effects. As a consequence, some of the most valuable theories in the different 

 branches of the natural sciences have been suggested, and are being worked out, 

 by means of the evidence afforded by these variations. The theory of evolution, 

 with all its ramifications, has been and is being developed along these lines. Since 

 the beginning of the nineteenth century, especially, the attention centered about 

 variations has been tremendous. Lamarck, Darwin, Mendel, and then Galton 

 were really the first to get the upper hand in the study and treatment of variations, 

 and more recently a rapidly enlarging group of workers in genetics have, by fresh 

 methods, gleaned a most fruitful harvest in this field. The methods themselves 

 have been most numerous and varied, and it is especially true of this subject that 

 its history is to be found in the history of its methods. At first lax and slip-shod, 

 they have gradually become, through the influence of the men just mentioned, 

 thorough and accurate. Probably the chief ones in present use are the statistical 

 and the experimental methods and their combinations. So, as time goes on, innum- 

 erable minutiae and data are gathered on every side and made to serve their part 

 in unraveling problems. A noteworthy instance of help afforded by such studies 

 is the more fundamental idea which we now have of the biological conception of 

 the normal or type. This very necessary standard, though even now far from 

 finally understood, has developed in the minds of men from a very rigid concept 

 into a far more plastic and adaptable principle, mainly through the insight gained 

 by variation study. 



Very often these studies may be applied with profit to specialized problems. 

 An example of this is the frequent and rather interesting results obtained along 

 morphological lines in the higher animal forms in demonstrations of the persist- 

 ence in postnatal life of earlier phases of development, which, as a rule, become 

 changed or obliterated during the course of growth. The present investigation 

 deals with the variability throughout the spinal column in respect to incomplete 

 union of the posterior laminae of the vertebrae. Associated with this subject is the 

 question of its relation to the pathological condition of spina bifida. The incom- 

 plete ossification of the adult vertebral spinous processes is also an example of a 



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