378 TRACING OF IMPULSES. 



spinal nerves, and ascend through the posterior column as far 

 as the eighth thoracic segment and then through the fasciculus 

 gracilis, or, entering above the eighth thoracic segment, they 

 ascend through the fasciculus cuneatus. In either case they arrive 

 in one of the nuclei of the posterior column, namely, the nucleus 

 funiculi gracilis or the nucleus funiculi cuneati. Thence the im- 

 pulses may proceed either by a direct or by an indirect route. 



(1) The direct route carries the impulses by way of the medial 

 fillet through the sensory decussation of the medulla, the formatio 

 reticularis of pons and mid-brain, to the lateral nucleus of the 

 thalamus, from which they are conducted by the cortical fillet 

 to the somaesthetic area of the cerebral cortex. In their last 

 stage the impulses run from the thalamus through the internal 

 capsule and corona radiata to the posterior central gyrus in the 

 equatorial zone of the hemisphere. 



(2) Indirect Route. By that route impulses from the nucleus 

 funiculi gracilis and nucleus funiculi cuneati run to the cortex 

 of the vermis cerebelli superior through the external arcuate fibers ; 

 then on, through the brachium conjunctivum, to the red nucleus 

 and thalamus. They traverse the restiform body of the same 

 side, by way of the posterior external arcuate fibers; or, by way 

 of the anterior external arcuate fibers, they traverse the fillet 

 decussation of the medulla and the opposite restiform body to 

 reach the vermis cerebelli superior. From the cerebellar cortex, 

 the impulses continue through cortical axones to the nucleus 

 dentatus, whose axones conduct them to the red nucleus and 

 thalamus of the opposite side. The greater number, therefore, 

 cross over in the tegmentum of the mid-brain. Their course 

 from the red nucleus and thalamus is through the cortical fillet 

 to the cortex. 



These impulses from the spinal nerves go to the upper two- 

 thirds of the posterior central gyrus, those from the lower extrem- 

 ity to the upper third and those from the arms to the middle 

 third (Spiller). 



Through Cerebral Nerves and Medial Fillet (Fig. 107). 

 As crossed fibers from the terminal nuclei of the trigeminal, the 

 vestibular, the glossopharyngeal and the vagus nerves join the 



