21 2 



above, in proportion to the degree of tlie activation of the osteo* 

 genetic potency contained in it. 



Tiie figure represents 4 human atlasforms A, B, C, and D. The 

 parts that have originated with certainty from the semi-sclerotome 

 hi are represented black; those of which this is very probable and 

 for which in many cases the region of extension can be limited 

 are hatched. 



A gives the scheme of the normal atlas without any variation. 

 We find in it, as belonging with great probability to the semi-segment 

 \a, the most cranial part of the central part of ihe posterior arch. 



Fig. 6. 



In B we find the ponticuli posteriores occurring bi-laterally re- 

 presented black; the part of the arcus postei-ior lying between the 

 two places of insertion of the ponticuli into the posterior arch is 

 hatched as in A. The part of the atlas belonging to semi-segment 

 \a represents now an arch lying between the posterior rim of the 

 massae laterales and assimilated with it and with the central part 

 of the arcus posterior. 



C differs from the preceding form only by the occurrence of the 

 ponticuli laterales, likewise represented black, by which the osseous 



