120 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



In the beginning of to-day's lecture you learned that cer- 

 tain fibres of the posterior commissure curved backward. These 

 fibres, together with others which arise in the depths of the 

 inter-brain, are met with as a fine fasciculus ventrad of the 

 anterior oculo-motor nucleus. As we pass back, this fasciculus 

 progressively increases in size. There are added to it numerous 

 fibres from the nucleus of the oculo-motor. We shall, from 

 now on, meet with the triangular cross-section of this bundle, 

 which is composed of fibres from such various regions on every 

 transverse section of the brain, from the level of the corpora 

 quadrigemina down to the beginning of the spinal cord. This 

 bundle is called the fasciculus longitudinalis posterior. Inasmuch 

 as fibres are given off along the whole course of this bundle to 

 the nerve-nuclei, as can be plainly seen in embryos of the sixth 

 to seventh month, when few other fibres are medullated, and, as 

 this bundle projects farther back than the nucleus of the abdu- 

 cens, it is probable that the fasciculus longitudinalis posterior not 

 onlv contains the fibres of communication between the nuclei 







of the ocular muscles, but that it also contains fibres to other 

 cranial nerves. Flechsig is also of this opinion. I have never 

 succeeded in tracing this fasciculus farther than the nucleus of 

 the oculo-motor previous to the ninth month. Series of longi- 

 tudinal sections stained Avith hrematoxylin (one of which is 

 represented on preceding page) are decisive. Not all fibres of 

 the fasciculus longitudinalis posterior receive their medullary 

 substance at the same time. 



In the neighborhood of the posterior qnadrigeminal body 

 there is an interchange of fibres between the two fasciculi longi- 

 tudinales posteriores. By this means there is established a com- 

 munication between the oculo-motor and the trochlear on one 

 side and the opposite abducens. 



The numerous systems of fibres which run their course in 

 the region of the corpora quadrigemina can only be differen- 

 tiated by studying the development of their medullary sheaths. 

 I should therefore dislike extremely, gentlemen, to close these 



