NERVOUS SYSTEM 



101 



are the enumerations for the myelinated fibers in the ventral 

 roots (Hatai, '03 b). 



It was found that the number of myelinated fibers in the 

 ventral roots diminishes from sections near the spinal cord to 

 those near the spinal ganglion. The amount of the diminu- 

 tion decreases with the age (body weight) of the rat. The in- 

 crease in the number of cells in the spinal ganglia from the small 



TABLE 61 



Number of ganglion cells and number and size of myelinated root fibers in spinal 



nerves from three levels of the spinal cord at five ages (body weights} 



Results from Tables II, VI and VIII combined Hatai ('02) 



Also data on ventral root fibers from Hatai ('03 b) 



to the large rats is certainly due in part to the fact that in the 

 small animals some of the smallest ganglion cells escape enumer- 

 ation. 



The increase in the number of myelinated fibers in the spinal 

 roots with advancing age is considered to be due, mainly, to 

 progressive myelination. Both roots at maturity still contain 

 functional fibers without myelin sheaths (Ranson, '06). 



