IL'S 



DK ALEXANDER BRUCE 



9. The lateral horn is not fully constituted above the lower half of the first dorsal 

 segment. This horn is not a transition from the lateral part of the anterior horn, but 

 is a new and independent formation. It is represented in C. 8 and the upper part of 

 D. 1 by the outlying cells of the intermedio-lateral tract. 



10. The lateral horns of the two sides may show a want of symmetry in size and 

 form, notably in the lower dorsal and lumbar regions. In the tenth, eleventh, and 

 twelfth dorsal segments the apical cells lie in a plane posterior to the central canal. 



1 1 . The middle cells described by Waldeyer do not form any part of the inter- 

 medio-lateral tract. 



12. The cells of the intermedio-lateral tract vary in size from 12 /x to 60 /u. 



13. The apical and reticular cells cannot be distinguished by any essential 

 difference in their form, size, or structure. Large and small cells lying in close juxta- 

 position may be present in both series in any one section. It has not been found that 

 any group is composed entirely of large or of small cells. Large cells are relatively 

 more numerous towards the lower end of the tract, but they are present alike in the 

 apical and in the reticular series. 



14. The number of cells in the intermedio-lateral tract is vastly greater than has 

 hitherto been recognised. The following are the total numbers counted in each 

 segment : — 





Left. 



Eight. 



C. 8 



595 



429 



D. 1 



1,867 



1,720 



D. 2 



3,931 



3,635 



1). 3 



7,297 



7,471 



D. 4 



3,623 



3,803 



I). 5 



7,958 



7,407 



D. 6 



8,105 



8,030 



D. 7 



8,739 



8,282 



D. 8 



6,223 



5,943 



I). 9 



9,011 



8.987 



I). 10 



8,903 



10,203 



D. 11 



6,261 + 



6,498 + 



I). 12 



7,888 



8,545 



L. 1 



7,053 



6,765 



L. 2 



1,123 



1,464 



Total 



$,577 



89,182 



These figures are certainly below the total number. 



15. The cells of the intermedio-lateral tract do not form a continuous column, but 

 occur throughout the tract in groups or clusters. 



1 6. These groups are not symmetrical on the two sides, although they may present 

 a general resemblance to each other. There appears to be a larger number of cells on 

 the left side in the lower cervical and upper dorsal regions. In the tenth dorsal 

 segment there is a large excess on the right side. 



