Hardesty, spinal Nerves of the Frog. 339 



vidual regularity between the increase in the weight of the 

 frog and the number of fibers forming the distal excess, yet 

 when the entries are separated into three successive groups 

 according to body-weight, the averages for the distal excess 

 show an increase as the animal increases in weight. For the 

 seven smaller frogs, the average distal excess is 114; for the 

 five medium sized frogs, 150, and for the five larger, the aver- 

 age is 197. 



It must be remembered that of the total number of fibers 

 contained in all the spinal nerves of a specimen, the proportion 

 of those contained in a given nerve is by no means a fixed one. 

 The two nerves of the same pair even often vary to such an 

 extent that the difference is noticeable to the naked eye. That 

 the number of fibers in the dorsal branches does not increase 

 in the same progression as the animals do in weight is probably 

 to be connected with this fact. 



Again, as bearing upon the cause of the distal excess, 

 Table II suggests also that the distal excess cannot be largely 

 due to a double counting of fibers on the distal side of the 

 spinal ganglion. The argument is the following : it is known 

 that fibers from the sympathetic system enter into the spinal 

 nerve by way of the ramus cammunicans and pass to the spinal 

 ganglion. It is now known also for both mammals and the 

 frog, that some of these sympathetic fibers are medullated, and 

 would therefore be counted as such. The possibility is that 

 some of these medullated sympathetic fibers may neither pass 

 on to the central system nor terminate in the spinal ganglion, 

 but, instead, may pass from the trunk, uninterrupted through 

 the distal portion of the ganglion and out again through the 

 dorsal branches. This being the case such fibers would be 

 counted twice, once in the trunk and once in the dorsal 

 branches. However, if the distal excess were due to the exist- 

 ence of such an arrangement of fibers, then the excess would 

 increase as the number of fibers in the dorsal branches increases. 

 The table shows that for the 6th. nerve at least, the distal ex- 

 cess and the number of fibers contained in the dorsal branches 

 display no tendency to parallel variation (columns 4 and 5). 



