382 TRACING OF IMPULSES. 



temperature impulses. These impulses enter the gray crescent 

 of the cord, on both sides, through the posterior nerve roots. A 

 large number decussate via the posterior nerve roots in the gray 

 commissure; the rest decussate in the first stage of the ascending 

 tracts, crossing in the white anterior commissure, and run upward 

 through the spino-thalamic and ascending anterior cerebello- 

 spinal tracts of the opposite side ; they run to the thalamus and to 

 the cortex of the superior worm of the cerebellum. In the cord they 

 ascend along the lateral surface. They run dorsal to the olive in 

 the lateral area of the medulla oblongata, and through the lateral 

 part of the formatio reticularis of the pons to the angle in Gowers's 

 tract situated near the isthmus. From the angle, just below the 

 quadrigeminal bodies, the cerebellar impulses run backward with 

 the tract through the superior medullary velum to the cortex of 

 the vermis cerebelli superior; the remainder run upward to the 

 thalamus, and from that to the posterior central cortex. The 

 common course of sensory impulses from the cerebellar to the 

 cerebral cortex is, as already described, through nucleus dentatus 

 and brachium conjunctivum to opposite red nucleus and thala- 

 mus. Having arrived in the thalamus, they proceed thence by 

 the cortical fillet to the somaesthetic cortex. 



Certain fibers of the ascending anterior cerebello-spinal tract 

 diverge from the others, in the medulla oblongata, and terminate 

 in the inferior lateral nucleus. Impulses of pain and temperature, 

 following the same course, enter the lateral nucleus, and are carried 

 on through the restiform body to the cerebellum by the tract 

 from the lateral nucleus to the cerebellar cortex, thence to the 

 somaesthetic area as previously given. 



Through Cerebral Nerves and the Spino-thalamic Tract 

 (Fig. 108). Pain and temperature impulses are transmitted by 

 certain fibers of the vagus, glossopharyngeal and trigeminal nerves 

 to their terminal nuclei. From those nuclei they .are conducted 

 by axones which probably enter into the spino-thalamic tract, 

 and, perhaps, into the ascending anterior cerebello-spinal tract, 

 to the thalamus and to the cerebellar cortex. The path from 

 either point to the posterior central gyrus is now familiar. 



The Short Fiber Paths. What special varieties of common 



