Ingbert, Ventral Roots of Spinal Nerves. 229 



In Table VI attention is called to the following points : 



1. The total number of nerve fibers in the ventral roots of 



the left spinal nerves is 203,700. 



2. The total number of nerve fibers in the dorsal roots of 



the left spinal nerves is 653,627. 



3. The ratio of the number of nerve fibers in the ventral 



and dorsal roots is 1:3.2. 



4. The number of fibers in the dorsal root C. IV and the 



ventral root C. Ill is small. 



5. The ratio between the number of nerve fibers in the 



ventral and dorsal thoracic roots (I-XII) is, on the 

 average, about 1:2. 



6. The number of nerve fibers in the largest ventral cervi- 



cal roots (C. V, VI) is twice the average number of 

 nerve fibers in the ventral thoracic roots. 



7. The number of nerve fibers in the largest dorsal cervi- 



cal roots (C. VII, VIII) is nearly five times the aver- 

 age number of nerve fibers in the dorsal thoracic 

 roots. Hence in the nerves supplying the arm, the 

 great gain has been in the number of fibers in the 

 dorsal or sensory roots. 



8. The number of nerve fibers in the largest cervical roots, 



both ventral and dorsal, is greater than that in the 

 largest lumbo sacral roots, ventral and dorsal. 



9. The arm, relatively to its weight of muscle, is better 



supplied with motor nerve fibers than is the leg. 

 10. The arm, relatively to its dermal area, is better supplied 



with sensory nerve fibers than is the leg. 

 In Figure 7 are given curves based on the absolute num- 

 ber of fibers in the ventral and the dorsal roots. They show in 

 a very striking manner the great numerical increase in the sen- 

 sory fibers innervating the limbs, while the number of motor 

 fibers at the corresponding levels is but slightly increased. 



That the difference between the number of fibers in the 

 ventral and dorsal thoracic roots (trunk) is so small, is what 

 might be expected. That the neck should show an increase in 

 the nerve fibers in the dorsal roots, does not require much com- 



