110 DR ALEXANDER BRUCE 



results arrived at were then compared, and any discrepancies were considered and cor- 

 rected. In this way greater precision as to the lateral boundaries of the tract and the 

 number of its cells was arrived at than would have been possible for a single observer. 

 The results of the finally corrected enumeration were then plotted graphically on the 

 diagram (PL I.). I am satisfied that the numbers are in no case excessive.* 



In C. 8 and D. 1, and in D. 2 (upper part"), the enumeration of the cells of the inter- 

 medio-lateral tract presented no particular difficulty. They formed very compact and 

 sharply circumscribed clusters, and their form and arrangement were so different from 

 those of any of the motor cells of the anterior cornu which were adjacent to them that 

 there was not the slightest difficulty in distinguishing the one from the other. This 

 was true in C. 8 and upper D. 1, where the cells lay behind the lateral part of the 

 anterior cornu, and in lower D. 1 and upper D. 2, where they formed a group limited 

 to the apex of the lateral horn proper. In the enumeration of the cells which lay 

 between the lower part of D. 2 and the lower extremity of the tract, two difficulties 

 were met with — one from the frequent absence of definition of the inner margin and 

 the other from the want of precise information as to the posterior limit of the tract. 

 On the inner aspect of the tract there were frequently seen small polygonal cells, 

 sometimes in fairly compact groups, sometimes as more scattered cells. These, which 

 evidently corresponded to the " Mittelzellen " of Waldeyer, sometimes approached 

 very closely to the cells of the intermedio-lateral tract, but with care they could 

 generally be separated from the latter. After a short training in the enumeration of 

 the cells, there was generally a close agreement between the various observers as to 

 the limits of the intermedio-lateral tract and the Mittelzellen. There seemed little 

 doubt that the Mittelzellen did not represent a part of the intermedio-lateral tract. 



The second difficulty, that of determining the posterior limit, was a much more 

 serious one. It arose from the fact that groups of cells of a character practically 

 identical with that of those found at the tip of the lateral horn were situated at the 

 margin of the grey matter, either underlying or partially entering into the formatio 

 reticularis, and extending as far back as the level of the posterior margin of Clarke's 

 column, or even further. In certain sections this series of cells (which will be referred 

 to in future as the reticular cells, from their relation to the formatio reticularis) seemed 

 absolutely distinct and separate from that situated at the apex of the lateral horn (the 

 apical cells). In consecutive sections it was found that the interval between the two 

 sets of cells lessened gradually until they came to approach each other closely, and 

 even to fuse so completely that it became impossible to distinguish the one from the 

 other. It was also observed that, almost without exception, the number of the apical 

 cells and that of the reticular cells rose and fell together ; when the one reached its 

 maximum so did the other, and vice versa. At first I was inclined (Rev. Neurol, and 



* At the upper and lower limits of each segment one or more sections were generally lost, owing to causes which 

 could hardly he avoided. In D. 11 some fifty sections were rendered useless owing to an accident from a fire which 

 occurred in the laboratory when the work was in progress. With these exceptions the sections were practically 

 continuous. 



