THE FASCICULUS CEREBRO-SPINALIS IN THE 



ALBINO RAT 



S. WALTER RANSON 

 The Anatomical Laboratory of the Northwestern University Medical School 



TEN FIGURES 



It is well known that the fasciculus cerebro-spinalis, more 

 commonly called the cortico-spinal or pyramidal tract, does not 

 occupy the same position in the spinal cord in all orders of 

 mammals. But, according to the animal which is being studied, 

 it may be found in any one or two of the three funiculi of the 

 cord. From its constant position in the ventro-medial portion 

 of the medulla it passes in the rat to the opposite posterior funicu- 

 lus of the spinal cord; while in the mole it runs without decussa- 

 tion into the anterior funiculus of the same side. In the cat it 

 decussates into the opposite lateral funiculus, while in man a part 

 of the fibers go over into the opposite lateral funiculus and a 

 smaller part run without decussation into the homolateral ante- 

 rior funiculus. 



There have been published a large number of articles dealing 

 with such variations in the position of the pyramidal tract, and 

 with the corresponding variations in the pyramidal decussation; 

 but very little attention has been paid to the character of the fibers 

 of which this fasciculus is composed. A study of sections of the 

 spinal cord of the rat, guinea-pig, rabbit and cat prepared by the 

 puridine silver technique has brought to light great differences 

 in the pyramidal fibers in these different animals. The varia- 

 tions in the size of the axons and in the degree to which the myelin 

 sheaths are developed are no less striking, and probably more 

 significant, than the variations in the position which the tract 

 as a whole assumes. It is with the characteristics of these fibers 

 in the white rat that this paper is primarily concerned and we 



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THE AMERICAN JOURNAL OF ANATOMT, VOL. 14, NO, 4 

 MAY, 1913 



