ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 127 



section 130 there are small groups of 3 or 4 cells, and beyond this there may be other 

 single cells whose nature it is impossible to determine with certainty. The cells lie at 

 the margin of the grey matter, which is now in front of Clarke's column. There is no 

 apex to the lateral horn, and no distinct definition in the three groups, apical and 

 reticular. There are a few outlying cells below the second lumbar segment. 



A few cells are found in the third lumbar segment, which perhaps correspond to the 

 intermedio-lateral tract, but the nature of which cannot be definitely determined. 



Conclusions. — From the examination of the graphic representation of the cell-groups 

 and of the microscopic sections, the following conclusions may be drawn as to the 

 distribution of the cells of the intermedio-lateral tract : — 



1. The intermedio-lateral tract may be defined as a tract composed of a special 

 series of nerve-cells, situated at the outer margin of that portion of the grey matter 

 which lies between the anterior and posterior cornua. These cells are not necessarily 

 limited to the lateral cornua. 



2. Within the spinal cord the tract is found in three regions : ( 1 ) in the upper 

 cervical region as low as C. 4 ; (2) in the lower cervical, the dorsal and the upper 

 lumbar regions; and (3) in the lower sacral region (below the lower part of the third 

 sacral segment). 



3. It is absent in the cervical enlargement from C. 5 to C. 7 inclusive, and in the 

 lumbo-sacral region from L. 3 to the upper part of S. 3 inclusive. 



4. In that portion of the tract which is at present under consideration — viz., the 

 second of the above-mentioned divisions — its component cells are found mainly in two 

 positions : (a) in the lateral horn proper, or in analogous positions above the level at 

 which the lateral horn is fully constituted ; and (b) along the margin of that part of the 

 grey matter which is in immediate relationship to the formatio reticularis, and also 

 among the strands of the formatio reticularis itself. For convenience of description 

 and reference these may be distinguished as the apical cells and the reticular cells. 



5. The apical and reticular cell-systems have not a coextensive longitudinal 

 distribution. 



6. The apical cells are found between the middle of the upper half of the eighth 

 cervical segment and the lower end of the second lumbar, or the extreme upper part of 

 the third lumbar segment. 



7. The reticular cells are first met with in the lower half of the second dorsal 

 segment, and have the same lower limit as the apical series. They are not present in 

 the cervical enlargement. 



8. The upper part of the apical cell-series is composed of cells which are either 

 situated in the white matter at some little distance behind the lateral part of the 

 anterior horn, or are applied more or less closely to the grey matter. In all cases the 

 cells are distinct from the large motor cells in their position, size, form, and grouping 

 No transitional forms are anywhere found between the cells of the two series. 



