no Journal of Comparative Neurology. 



XII. Explanation of Plates. 



PLATE VI. 



The ten spinal nerves of Rana virescens. Left side. Drawn to scale and 

 enlarged six diameters. 



The Roman numbers indicate the number of the nerve. 



The Arabic numbers indicate the levels at which the sections were taken 

 for the enumeration of fibers recorded in Tables I and II. The Arabic number 

 6 indicates the region at which the sections of the dorsal branches were taken. 

 In case of the Vlllth and IXth nerves the branches are here so arranged that 

 the transverse section of the trunk may also involve a transverse section of the 

 branches. 



C. — Ramus communicans. 



D, r. — Dorsal root. 



V. r. — Ventral root. 



PLATE VII. 



Figs. 1-6. A series of transverse sections which show a growing fiber. 

 Taken from ventral root of Vlth nerve of frog used in Table I. The series, 

 beginning at Fig. i, passes toward the spinal cord and includes a length of 

 about 30 micra. 



The smallest fiber of the group, the growing fiber, makes its first appear- 

 ance as a brown ring and soon acquires its medullary sheath. 



Camera drawings. Magnification, 466 diameters. 



Fig. 7. Automatic registering apparatus used in counting technique. 

 When rod containing the needle is pressed inward the machine records. 

 y^ natural size. 



plates VIII TO XIII. 



General explanation : 



Plates IX, XI and XIII represent sections from the ventral root of the 

 Vlllth nervt of a frog of 48.2 grams. The plates are made from the identical 

 photographs employed for the enumeration of the fibers of this root as recorded 

 m Table I and correspond respectively to columns A, B and C of that table or 

 to levels I, 2 and 3, Plate VI. 



