AX ATOMY IN A NUTSHELL. 435 



(6.) In this route impulses pass up (Power's tract (fasciculus spino- 

 cerebellaris ventro-lateralis) by neurones of the second older to the mid-brain. 

 From here they reach the superior worm by the way of the superior peduncles 

 of the cerebellum. The remainder of the route is the same as that in route 4 

 and 5. Neurones of the first order give collaterals to cells of the gray matter. 

 The indirect route may take six neuroxk SYSTEMS to complete its course while 

 the direct takes only three. This route is indirect because it passes through 

 the cerebellum. 



LESSON CXXX. (Plate CCXXXI). 



The motor impulses, which are efferent (centrifugal) take the following 

 routes : 



(1.) By the way of the pyramidal tract without passing through 

 the cerebellum. This route is direct. 



Impulses in this route pass from the cortex through the corona radiata. 

 internal capsule, and pyramidal tracts to the lower end of the medulla by neu- 

 rones of the first order. From the lower end of the medulla the fibers pass in 

 the following ways: (a) most of them cross to the opposite side in the decussa- 

 tion of the pyramid to descend in the crossed pyramidal tract (fasciculus cere- 

 bro-spinalis lateralis) to end in the gray matter of the anterior horn. (1>) some 

 of the fibers descend in the direct pyramidal tract (fasciculus cerebro-spinalis 

 ventralis) to end in the gray matte r of the anterior horn, (c) the remaining fibers 

 d< set rid in the crosst d pyramidal tract of the same side to e nd in the gray matter 

 of the anterior horn. From the cells in the gray matter of the anterior horn neu- 

 rones of the second order carry impulses to the muscle. Thus we see that two 

 neurone systems will carry a motor impulse from the cortex to the muscle 1 . 



(2.) By the way of corpus striatum and mid-brain without passing 

 THROUGH THE CEREBELLUM. This route is direct. 



These- impulses pass by neurones of the first order to the- corpus striatum. 

 Most of these' come from the frontal region. They now pass by neurones of the 

 se'e-eind order to the' mid-brain. From the' mid-brain impulses pass by neurones 

 of the third order by the' antero-lateral de scending tract to end in the' gray matter 

 of the' 'anterior horn. Neurones of the fourth order now carry the impulse' to 

 the muscles over the' anterior roots of the spinal nerves. 



(3.) By way of the pyramidal TRACT, NUCLEI PONTIS, CEREBELLUM, BUL- 

 BAR nuclei. This route passes through the cerebellum therefore it is an in- 

 direct route. Impulses pass by the neurones of the first order through the 

 corona radiata, internal capsule, and pyramidal tract to the pons. From the- 

 pontis nuclei impulse's pass by the' middle' peduncle's to the' cortex of the opposite 



side of the- cerebellum. From here neurones of the third order carry the im- 

 pulses to the' dentate' nucleus. Neurones of the fourth order pass from the 

 dentate' nucleus to the bulbar nuclei. Neurones of the fifth order pass from 

 the bulbar nuclei to end in the gray matte r of the and rior horn and from here 



neurones of the' sixth order pass to the muscle s. 



