THE PONS FINAL REVIEW. 219 



disturbances of circulation are also more often caused by affections of the 

 oblongata. 



Almost all these symptoms may be caused in rare oases by disease in the 

 cerebrum, inasmuch as injury to the central tracts of the cranial-nerve fibres is 

 followed by paralysis, just as is injury to the nucleus or to the peripheral nerve. 

 Paralysis of certain muscles supplied by nerves originating in the oblougata can 

 only he ascribed to disease of the latter when simultaneous muscular atrophy 

 appears, and an injury to the trunk of the nerve, outside the central organ, can 

 be excluded. 



Gentlemen : Our task is nearly done. A great number of 

 important systems of fibres have been studied, both with regard 

 to their relations to the central gray ganglia and to their course 

 from the fore-brain down to the termination of the mid-brain, 

 or from the spinal cord up to the same level. Still, it seems 

 advisable again to examine a few of them briefly, either because 

 they are of particular importance in connection with physiology 

 or pathology, or because the comprehension of their whole 

 course was rendered more difficult on account of their being 

 traced, for didactic reasons, in an opposite direction after Lecture 

 VII. Let this short recital serve as your guide in a sort of 

 review, which you can easily undertake with the aid of the 

 illustrations. 



1. The pyramidal tract: The most important tract of 

 notor innervation arises from the upper two-thirds of the central 

 convolutions and the paracentral lobule, and runs to a point 

 behind the knee of the internal capsule. From there it passes 

 into the pes pedunculi, where it occupies the middle third. In 

 the pons its fibres are but little divided by the transverse fibres 

 of the latter. 



After emerging from the pons its fibres lie in two thick 

 bundles on the ventral surface of the oblongata. In this position 

 they pass to the spinal cord. Here the great mass of the fibres 

 cross to the opposite lateral columns ; a smaller portion (anterior 

 pyramidal tract) remains on the same side. Both these masses 

 of fibres enter into relations with the cells of the anterior horns 

 of the side opposite their cortical origin in the brain. From 

 these cells the motor roots arise. Compare Figs. 44, 47, 56, 62, 



