The Pyramid Tract in the Canadian Porcupine. 5 



This disposition of the pyramid tract fibers is not found in all 

 mammals however. In the guinea-pig (v. Bechterew, Reveley), 

 mouse (v. Lenhossek), rat (Flechsig, King) and squirrel (Weigner), 

 and in the monotremes and marsupials (Kolliker and Ziehen), the 

 crossed fibers run in the dorsal and not in the lateral column of 

 the cord. 



In the spring of the present year, I obtained some full-grown 

 porcupines with the object of investigating the course of the 

 pyramid tract fibers in this animal. The left motor cortex was 

 located by electrical stimulation and then extirpated in the usual 

 way. At the end of about a fortnight after the operation in each 

 case the animal was killed, the brain and cord removed, stained 

 by the Marchi method and sectioned at all levels. A full descrip- 

 tion of the resulting degenerations will be published later; in this 

 preliminary communication only the most important points will 

 be mentioned. 



In the internal capsule, pes pedunculi, pontine bundles and 

 upper levels of the medulla oblongata, the fibers occupy the usual 

 positions and no special comment is called for, but in the lower 

 part of the medulla oblongata the arrangement is peculiar, and 

 nothing similar, so far as I know, has been hitherto described in 

 any other animal. 



At the decussation of the pyramids most of the degenerated 

 fibers cross the median raphe, pass backwards through the gray 

 matter, and take up a position in the dorsal column of the opposite 

 side occupying the ventral portions of the fasciculi of Goll and 

 Burdach. A few of the crossed fibers curve outwards and enter 

 the opposite lateral column of the cord. A very considerable 

 number of fibers, however, remain uncrossed and are continued 

 into the cord, forming a comparatively large and compact bundle 

 in the ventral column extending along the margin of the anterior 

 median fissure. Some uncrossed fibers are also found in the 

 dorsal column of the same side but these are very scanty. 



In this animal, then, the fibers of the anterior pyramid on 

 entering the spinal cord are divided into four fasciculi, two crossed 

 and two direct, viz: the crossed dorsal pyramid tract, the crossed 

 lateral pyramid tract, the direct ventral pyramid tract, and the 

 direct dorsal pyramid tract. Of these the crossed dorsal and 



