PRENATAL GROWTH OF SPINAL CORD 47 



The decrease in the relative growth-rate with age is also shown 

 by the decline in the percentage which the spinal cord forms of 

 the entire body. This agrees with the rate of absolute growth in 

 that as the age increases the percentage becomes relatively 

 smaller. Vierordt ('06) gives 0.18 per cent of the total body 

 weight for the spinal cord in the newborn and 0.06 per cent in the 

 adult. These figures added to my results show that the decrease 

 in growth-rate of the spinal cord continues through prenatal into 

 postnatal life. This agrees with the conclusion reached by 

 Jackson ('09 b). 



4. Growth of the various regions 



a. Cervical region. The different regions in the spinal cord 

 show in their rates of growth some slight differences when com- 

 pared with the rate of growth of the entire cord. The cervical 

 region exhibits a slower rate of growth than the whole cord up to 

 the 31 mm. embryo, while from here to the end of the first half of 

 prenatal life (150 nrna. embryo) it slightly exceeds the growth rate 

 of the whole cord. The cervical region during this time increases 

 approximately 175 per cent, while the entire cord during the same 

 period increases less than 166 per cent. 



The relative amounts by volume which the different regions 

 form of the entire cord are given in table 1. The cervical region 

 in the 11 mm. embryo constitutes 37 per cent of the entire cord. 

 This is probably somewhat too large owing to the obliquity of the 

 cord in this region. There is a slight decrease to about 28 per cent 

 in the mid-fetal cord (150 mm.). In the two-year-old child it is 

 relatively larger, forming 36 per cent of the entire cord. There 

 is a decrease to 31 per cent between this and the adult stage, 

 which seems to correspond to the increase in the thoracic region 

 of the cord. 



In area of cross-section, using the 5th cervical segment for com- 

 paring the growth of the cervical region, it is observed (tables 3 

 to 6, also figs. 1 to 12) that the area increases as growth in volume 

 proceeds. However, a comparison of the 17 mm." and 31 mm. 

 embryos shows that the cross-sectional area increases only about 

 60 per cent while the volume in the same period increases over 100 



