316 S. Simpson, 



part, and of the crossed pyramidal tract in tlie spinal cord. When 

 the motor decussation proper is reached, bundles of fibres are ob- 

 served to come off from the postero-internal angle of the degenerated 

 pyramid, and after crossing the middle line, to pass backwards towards 

 the lateral portion of the grey matter around the central canal, and 

 then to curve more outwards and become lost as they turn caudal- 

 wards in their passage towards the lateral column (crossed pyramidal 

 tract) of the spinal cord. I have seen very few fibres passing in a similar 

 direction from the degenerated pyramid towards the same side (homo- 

 lateral) until the middle of the decussation is reached, and from this level 

 downwards these homolateral fibres increase in number (fig. 5. pi. XVI). 

 Eedlich [6] says these homolateral fibres come off in greatest abun- 

 dance from the middle "/^*^^ of the decussation. When this region 

 of the medulla oblongata (pyramidal decussation) is cut serially, they 

 are missed in several consecutive sections and then appear again. 

 This is due to the fact that they come off in small bundles compar- 

 atively widely separated from each other verticali}^ The ratio be- 

 tween the decussating and non-decussating fibres vary considerably in 

 the different animals, but the relative numbers can only be known by 

 counting the fibres on each side in sections through the upper cer- 

 vical cord, and not by comparing the two sides in any one section 

 through the decussation. Down to the level of the pyramidal decussa- 

 tion a few black dots had been observed in transverse sections of 

 the pyramidal tract of the side opposite to the lesion in several of 

 the earlier animals, but whether these represent degenerated fibres or 

 are merely accidental it is difficult to be certain. In material pre- 

 pared later in the research when more experience had been gained in 

 the technique, the degeneration was almost invariably wholly uni- 

 lateral down to the level of the decussation. 



In the cervical region of the spinal cord the degenerated crossed 

 pyramidal tract occupies a comparatively small rounded area (rela- 

 tively Miucli smaller than in the monkey) in the posterior part of the 

 riglit lateral column, close to the antero-lateral aspect of the i)osterior 

 liorii. and not reaching the margin of the section. From this tract, in 

 iiiHii}- of the cases, a few degenerated fibres are seen to pass in to- 



