52 MAX MAYO MILLER 



4. Growth of the various regions {figs. 6 to 12; tables I and 7 to 12) 



The cervical region of the cord contains relatively more gray 

 matter by volume than does the cord as a whole. In the 31 mm. 

 embryo the gray matter is 57 per cent of the cervical region, while 

 it is slightly less in the entire cord (55 per cent). This holds 

 true in all the embryos studied, and is seen, by the data on the 

 child and adult, to continue into postnatal life. The gray 

 matter of the cervical region reaches the maximum relative size 

 in the 31 mm. embryo, while in the entire cord the maximum 

 percentage of gray matter is in the 65 mm. specimen. The gray 

 matter in the thoracic region has practically the same rate of 

 growth as the gray matter in the cord as a whole up through the 

 stages examined. The gray matter in the lower regions grows 

 faster than the gray matter in the entire cord up to the 17 mm. 

 embryo, but it grows relatively slower during the rest of the 

 first half of prenatal life. 



C. WHITE MATTER 



1. Form (figs. 1 to 6) 



The various columns are indefinitely formed in the 11 mm. 

 embryo and later gradually assume their typical shapes and 

 relations to the gray matter. Even in the mid-fetal stage (150 

 mm.) the white matter still forms only a comparatively thin 

 layer surrounding the gray matter. 



2. Growth as a whole {table 1) 



The white matter shows a steady increase in the total amount 

 both absolutely and relatively from the youngest embryo exam- 

 ined to the adult, as shown in table 1. In the 11 mm. specimen 

 the white matter forms 13 per cent of the entire cord while in 

 the 150 mm. fetus (mid-fetal period) it constitutes 46 per cent 

 of the whole cord. In the child of two years it forms 73 per 

 cent and in the adult 80 per cent. This is considerably different 

 from the gray matter which, as we have seen, increases relatively 



