222 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



central sensory tract, or at least contains a good share of it. 

 (Figs. 62, 65, 66, 70, and 72). 



The fillet then passes back in the tegmentum of the cms, 

 the pons, and the oblongata. On its way it gives off fibres to 

 the opposite nuclei of the trigeminus, the acoustic, the glosso- 

 pharyngeal, and the vagus. (Figs. 127, 126, 125, 122, and 121). 



In the medulla oblongata a large share of the fibres branch 

 off and pass dorsad over the middle line to the nuclei of the 

 posterior columns, internal arciform fibres. (Figs. 120, 117, 

 115, 114, 111, 110, and 109.) 



The fibres of the posterior columns run caudad from the 

 nuclei of these columns. Opposite each spinal-nerve root a few 

 fibres are given off, which emerge with the root and enter the 

 cells of the spinal ganglion. From these cells the sensory nerve 

 arises. 



Those fibres of the fillet which are left after the tracts to 

 the nuclei of the posterior columns have been given off run 

 backward in the anterior and lateral columns of the spinal cord. 

 A number of these fibres pass off to the gray matter opposite 

 each sensory spinal nerve, traverse it, and enter the opposite 

 posterior horn. They are lost in the net-work of cells and fibres 

 at that point; from this net-work, however, a great number of 

 the sensory fibres arise. They all terminate directly in the 

 spinal ganglion, and from this the sensory fibres arise. (Figs. 

 102, 100, and 88). 



In this way connections are established between all the 

 fibres of the layer of the fillet and the nuclei which lie on the 

 opposite side. A portion decussate in the oblongata, the rest 

 only do so after reaching the spinal cord. From these nuclei 

 the fibres of the posterior roots are given off. 



You have seen that the motor nerves are connected directly 

 witli the cells of the anterior horn, and have learned that a 

 central tract, partly direct and partly crossed (the pyramids), 

 arises from the anterior horns. The direct part (lateral pyramidal 

 tract) passes across to the opposite side in the oblongata, and so 



