46 



MAX MAYO MILLER 



3. Groivth of the cord as a whole 



The total volumes of the spinal cords measured are shown in 

 table 1. From these data and volumes of the entire body (which 

 were known) ■ the percentages that the cords bear to the entire 

 body were calculated. They are as follows: 



1 Estimated 



The difference in the percentages obtained by Bonnot and 

 Seevers ('06) for the 11 mm., and Jackson ('09 b) for the 17 mm. 

 and 31 mm. specimens, and those by myself is quite marked. 

 Their results are given in parentheses, and are larger in every case. 

 This difference is due chiefly to a difference in technique. In 

 measuring the area of the various sections they took the border on 

 the outer edge of the meninges immediately surrounding the cord, 

 and passed directly over the anterior fissure and posterior sulcus, 

 while I in all cases measured on the surface of the spinal cord 

 proper, leaving out the meninges and following the various breaks 

 in the continuity of the outline. A small difference would be 

 expected due to this difference in technique. 



The absolute growth of the prenatal cord is very rapid in the 

 younger embryos as shown by the total volumes of the cords in 

 table 1. This is what is expected, since the neural tube or anlage 

 of the spinal cord develops very early in the embryo. The rate 

 of growth seems, in general, to decrease with the age of the embryo. 

 During the second and third months (11 mm. to 65 mm.), the cord 

 has increased thirty-six times, or 3600 per cent. In the fourth and 

 fifth months (65 mm. to 150 mm.) together the increase is only 

 approximately 160 per cent. 



