LECTURE XII. 



THE PONS FINAL REVIEW. 



GENTLEMEN : We reached, in our last lecture, that level of 

 the tegmentum which we discussed in the eighth lecture. A 

 few millimetres cephalad of the last section, the fibres of the 

 pes emerge from under the pons to pass independently to the 

 brain. In the medulla oblongata the pyramids are the only 

 structures which pass into the pes ; but from the ganglia of the 

 pons huge bundles of fibres emerge, which run in the median 

 and lateral portions of the crusta, and can be traced as far as 

 the cortex of the frontal, parietal, and temporal lobes. 



Now, again, we see the substantia nigra dividing the pes 

 from the tegmentum. 



The anterior cerebellar peduncles are lost in the red nuclei, 

 and in place of the velum medullary anticum the roof is formed 

 by the corpora quadrigemina. 



The reproduction of a few sections which have been given 

 before may recall to mind what was then said, and make clear 

 the transition from the pons into the quadrigeminal region. 

 (See Figs. 129, 130, and 131.) 



The symptoms which arise in diseases of the pons and ob- 

 longata are, from the manner in which they are grouped, a 

 pretty good proof of the correctness of our views of the 

 anatomical relations of these parts. 



Tracts are here crowded into a small space, which are of the utmost impor- 

 tance in movements of the muscles, in sensation, speaking, swallowing, etc. A 

 disease focus need be but small to cause many different symptoms here. 



The central motor and sensory tracts, which arise from the cortex as well as 

 from the inter- and mid- brains, pass through the pons and oblongata, and only 

 give off those fibres which go to the nuclei of the cranial nerves. 



Inasmuch as a break in the conductivity of these long tracts will cause the 

 same symptoms, whether it occur in the fore-, mid-, or hind- brains, we can only 

 suspect disease of the pons or oblongata if symptoms are at the same time present 

 which show that one or more of the cranial-nerve nuclei have been involved. 



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