66 Journal of Comparative Neurology. 



termination of the length of some of the nerve fibers arising 

 from the cells of origin situated in the ventral horns of the spi- 

 nal cord and in the spinal ganglia. 



The region chosen for the study of this extension of the 

 nerve fibers is, on the one hand, that formed by the roots of the 

 spinal nerves, and on the other, that formed by the spinal nerve 

 trunks as far as their union with the rami communicantes. The 

 study involves first, an enumeration of the fibers contained in 

 each nerve root at different levels, and second, a determination 

 of the number of fibers contained in a section of the trunk and 

 dorsal branches immediately distal to the spinal ganglion and in 

 a section of the trunk further distal. 



The animal examined was the common leopard frog, Ra?m 

 virescens. 



III. The Gross Anatomy of the Spinal Nerves. 



The gross appearance of the different spinal nerves when 

 dissected out and freed from adherent connective tissue is ex- 

 hibited in Plate VI. The sketches there produced are drawn 

 to scale. 



Passing from the Xth to the 1st nerve, three chief fea- 

 tures of variation are to be noted. 



I. The most marked variation is exhibited in the abund- 

 ance of the dorsal branches. It is seen that for the Xth these 

 branches are few, for the IXth they are more abundant, while 

 for the Vlllth there is seldom more than one, and this is rela- 

 tively very small and arises directly out of the mass of the gan- 

 glion instead of springing from the nerve trunk at the distal 

 end of the ganglion as it does in case of the IXth and Xth. 

 For the Vllth, again, the condition is much as it is in the IXth. 

 The dorsal divisions of the Vlth, Vth, and IVth are both rela- 

 tively and absolutely larger than those of any of the other 

 nerves. For the Ilird nerve the branches are less than for the 

 three nerves caudad to it, and the larger branches of it usually 

 arise out of the ganglion and at right angles to the long axis of 

 the nerve trunk. The llnd gives off many very small branches 

 but in a very irregular manner, while the 1st returns to the gen- 

 eral type of those most caudad. 



