SPINAL GANGLIA. 



521 



the motor root, and then turn back and descend again to the 

 junction of the roots, whence they pass along the posterior root 

 to the cord. These fibres are named the " recurrent sensory 

 fibres," and the recurrent sensibility of the anterior roots is not 

 regarded as any serious departure from Bell's law. 



The course of the secretory, etc., nerves probably follows that 

 of the motor channels at their exit from the cord. Their per- 

 ipheral distribution, and that of the vasomotor nerves, are inti- 

 mately connected with the sympathetic system, and will be con- 

 sidered further on. 



Of the function of the ganglia on the posterior roots of the 



FIG. 206. 





Section through spinal ganglion of a cat, showing ganglion cells interspersed between 

 the fibres. (Low power.) 



spinal nerves but little is positively known. There is no evidence 

 of their being centres of reflex action, nor can they be shown to 

 possess any marked automatic activity. From the fact that, when 

 a mixed nerve is divided, the end cut off from the ganglion de- 

 generates after a few days, these ganglia are supposed to preside 

 over the nutrition of the tissue of the nerve itself. And if the 

 roots be cut, that part of the posterior root attached to the cord 

 degenerates, while the piece connected with the ganglion is well 

 nourished. This is not the case if the anterior root be divided, 

 but, on the contrary, that portion next the cord is well nourished, 

 while that going to join the posterior root is degenerated. 

 44 



