Hardesty, Medulla Spinalis of the ElcpJiant. 177 



mouse and bat, about 2 times that of the substantia grisea. By- 

 comparing columns 3 and 4 it will be seen that column 2 is but 

 another form of the ratios given in column 4, and that there- 

 fore the above statement will apply also to the ratios between 

 the areas of substantia grisea and the areas of substantia alba 

 contained in the sections. 



It is evident, then, that animals approaching each other in 

 size of body have similar ratios between the area of substantia 

 grisea and the area of medullated axones in transverse sections 

 of the intumescentia cervicalis. In the elephant, however, 

 much the largest animal in the first group, the area of medul- 

 lated axones exceeds the area of substantia grisea to a less ex- 

 tent than in any other of this group. 



2. The area of the substantia alba in the different sec- 

 tions (column 3) decreases more regularly and more rapidly 

 than the area of the corresponding substantia grisea, and in the 

 larger specimens, the area of substantia grisea is exceeded 

 to a greater extent by the area of the substantia alba surround- 

 ing it than is the lesser area of substantia grisea in the smaller 

 specimens. 



Reading columns 1,2, and 3 upward, it will be seen that 

 as the specimens increase in size the increase is due more to 

 the increase in the area of the medullated axones than to the 

 increase in substantia grisea. The cell bodies contained in the 

 substantia grisea give origin to a large proportion of the medul- 

 lated axones going to form the substantia alba (long and short 

 association and commissural pathways). A greater amount of 

 substantia grisea is coincident with a greater number of cell-bodies 

 situated in it. This greater number of cell-bodies must be coexis- 

 tent with the presence of a greater number of medullated axones 

 in the section : axones arising (i) in other levels and coursing 

 in the section to connect with the cell-bodies in the vicinity of 

 the section, and (2) axones arising from the cell-bodies them- 

 selves and passing to other levels of the medulla spinalis 

 or to the peripheral system. It has been shown that 

 the axone of the neurone even exclusive of the medullary 

 sheath may be many times the volume of the cell body giving 



