136 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



sensory trig-eminus, which may be considered as the 

 posterior root of the facialis, possesses a peripheral 

 ganglion (ganglion Gasseri), while the chiefly motor 

 facialis has no peripheral ganglion, Bell concluded 

 that the posterior roots of the spinal cord, which pos- 

 sess peripheral ganglia, are sensory, while the anterior 

 roots, which possess no ganglia, are motor. Bell 

 found (by means of vivisection) that division of the 

 trigeminus produces disturbances in eating in those 

 animals that take their food with the lips : these 

 disturbances are caused, naturally, by the weakness of 

 the corresponding muscles. 



We will add a word here concerning the import- 

 ance of the ganglion-cells for the preservation of the 

 axis cylinder. The axis cylinder may be regarded as 

 a protoplasmic extension of a ganglion-cell, which 

 lives only as long as it is connected with the cell. 

 Now the ganglion-cells of the dorsal roots are located 

 in the spinal ganglion, those of the ventral roots in 

 the ventral horns of the spinal cord. If the posterior 

 roots be severed, that part of the fibres which is con- 

 nected with the spinal cord degenerates, while the 

 part that is connected with the spinal ganglion is 

 preserved, and grows or regenerates. If the ventral 

 roots be severed the peripheral stump degenerates, 

 while the stump that is still connected with the spinal 

 cord is preserved and grows. We may mention here 

 briefly that the nerve-fibres of the posterior roots, 

 according to Golgi's school, are not fused with the 

 ganglion-cells of the posterior horns in the spinal 



