It has been sometimes found that stimulation of the anterior roots seemed to cause pain, as shown by the motion of other parts besides those to which this root was distributed; and it was believed that some sensory fibres must run in the anterior roots. But it has been found that if the corresponding posterior roots be cut these signs of pain when the anterior roots are stimulated are not shown. From this it has been concluded that the apparent sensory channels of the motor roots are nothing more than some sensory fibres which pass from the nerve trunk a little way up 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 peripheral distribution, and that of the vasomotor nerves, are intimately connected with the sympathetic system, and will be considered further on.

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

Fig. 207. Section through spinal ganglion of a cat, showing ganglion cells interspersed between the fibres. (Low power).

Two cells from the former seen under a high power, showing the fine protoplasm here and there retracted from the cell wall.

Fig. 208. Two cells from the former seen under a high power, showing the fine protoplasm here and there retracted from the cell wall.

Of the function of the ganglia on the posterior roots of the 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 degenerates 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 connected with the posterior root is degenerated.

It would thus appear that the trophic function of the ganglia is restricted to the sensory nerves, while the nutrition of the motor nerves is provided for by nervous centres situated higher up.