54 Journal of Comparative Neurology and Psychology. 



cide more nearly with the variations in the distal excess than do 

 the variations in the dorsal roots. 



8. With the increase in weight, the fibers on the distal 

 side of the spinal ganglion increase in number more rapidly 

 than do the sums of the dorsal and ventral roots. In proportion to 

 the fibers contained in them, the dorsal branches gain fibers at a 

 more rapid rate than any other part of the nerve. This more rapid 

 increase of the distal fibers is in some measure an expression 

 of the more rapid rate of increase of the distal excess. 



9. Supported by direct observations, the distal excess is 

 explained as due to three causes : (a) Centripetal medullated 

 fibers from the sympathetic system which enter the spinal gang- 

 lion to branch and terminate about the cells there ; (b) The bi- 

 furcation of ventral root fibers on the distal side of the spinal 

 ganglion ; (c) The bifurcation of the peripheral axone of the 

 spinal ganglion neurone. In most of the bifurcations observed, 

 one pioduct of the division joins the dorsal branches while the 

 other remains in the nerve trunk. The observed divisions of 

 the fibers of the dorsal branches themselves may take part in 

 producing the distal excess. There are some indications support- 

 ing the assumption that certain of the excess of cells in the spi- 

 nal ganglion may also contribute to the distal excess by sending 

 processes into the periphery but not toward the central system. 



10. With the increase in body weight the ventral roots of 

 the Vth, Vlth and IXth nerves gain fibers at a more rapid rate 

 than do the dorsal roots, and at a more rapid rate than the 

 nerve trunks considered separately. 



I I. With the increase in body weight there is an apparent 

 gain in the number of spinal ganglion cells in the three nerves. 

 Between the average weight of 14.2 grams and that of 5 1.6 

 grams the ganglion cells increase about 2 i ^r , or gain at the 

 rate of 27.8 cells per gram of weight. 



