114 Journal OF Comparative Neurology. 



IV. The Dorsal Roots. 



A. Total Number of the Dorsal Root Fibers at Different 

 Ages. 



The number of the fibers of the dorsal roots has been 

 enumerated by several investigators. Holl ('75) counted the 

 fibers in the two roots and the trunk of three of the lum- 

 bar nerves of the frog in order to compare the total number 

 of the fibers in the two roots with that of the corresponding 

 trunks ; Freud {'yS) in studying the relation of the dorsal root 

 fibers to the spinal ganglion cells made counts on Petromyzon ; 

 Stienon ('80) in studying the relation of the dorsal root fibers 

 to the cells of the spinal ganglion made two counts of the 

 fibers in the two roots and in the trunk ; Hodge ('88) counted 

 in the frog the number of fibers of the dorsal roots and the num- 

 ber of the cells in the spinal ganglia of several nerves in order to 

 show the numerical relation between the two; Birge ('82) made 

 counts on the dorsal and ventral roots and at the same time the 

 trunk of the several spinal nerves of the frog in order to com- 

 pare the numbers in these three different regions, as well as to 

 show the relative increase of the fibers and the cells in the an- 

 terior horn according to different weights of the frog ; Gaule 

 and Lewin ('96) counted the fibers contained in the two 

 roots and in the trunk and dorsal branches of three of the sacral 

 nerves as well as on the cells of the corresponding spinal gang- 

 lia of the rabbit, in order to determine the number in each case ; 

 BOhler ('98) undertook the problem in order to compare the 

 number of fibers with the number of cells in the spinal ganglion 

 in the frog ; Hardesty ('99) counted ui eight spinal nerves, the 

 two roots and trunks, in order to determine the number in each 

 case, and he further extended his studies ('00) on the frog in 

 order to compare the number of fibers in the same regions at 

 different seasons, but in this latter case, the Vlth. spinal nerve 

 was used exclusively ; Dale ('00) has made similar counts of 

 the fibers in some of the coccygeal, two thoracic and one lum- 

 bar nerve of the cat. All investigators (Hodge, Gaule and 

 Lewin, and Buhler) who have compared the number of cells in 



