ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 129 



17. These groups or clusters vary in size and form and in their distance from 

 each other. 



18. In each segment the cell-groups are arranged in a manner which may be 

 regarded as characteristic of that segment. 



19. The number of groups in each segment is somewhat difficult to determine in 

 some cases ; generally the number is fairly equal on the two sides. 



20. At the upper and lower extremities of the tract there is a tendency for the 

 groups to appear suddenly, to rise rapidly to a maximum, and then quickly to disappear 

 (see graphic chart). Towards the centre of the tract — below the fifth and above the 

 tenth dorsal segments — the groups are less separated from each other. They rise 

 slowly, persist for a considerable length, and diminish slowly. In this region the 

 maximum number of cells attained is never so great as towards the extremities of 

 the tract. 



21. There is a remarkable increase in the number of the cells in the third 

 dorsal segment. There is a marked transition in the form of the groups in the 

 middle of the fifth dorsal segment, and another at the middle of the ninth dorsal 

 segment. 



22. The intermedio-lateral tract has a vascular supply largely independent of that 

 of the motor cells of the anterior cornu. 



23. The segmentation of the tract into groups or clusters of cells is not due to 

 the distribution of blood vessels or of the root fibres, but is probably in some way 

 related to their function. 



Although the present communication is intended to be a purely anatomical 

 investigation, its main interest, of course, must be derived from our knowledge of its 

 function, and of the pathological changes which it undergoes in disease. 



The researches of Gaskell and Langley as to the outflow of the sympathetic fibres 

 show that the distribution of these coincides in a remarkable manner with the distribu- 

 tion of the cells of the intermedio-lateral tract. It is now certain that the column of 

 Clarke cannot be the source of the origin of these fibres, and if there is any spinal 

 centre at all it must, by exclusion, be either the " middle cells " of Waldeyer or the 

 intermedio-lateral tract, or both of these. 



This communication shows that where there is the greatest outflow of sympathetic 

 fibres there is the greatest number of cells in the intermedio-lateral tract. The cervical 

 sympathetic gets its largest supply of fibres from the portion of the cord included 

 between the eighth cervical segment and the fifth or sixth dorsal segments — segments 

 in which the groups are most rich in cells. Then the outflow of the splanchnics is 

 largest in the lower dorsal region, and here again the number of cells markedly increases 

 and the character of the groups changes. The researches of Anderson and Herring, 

 and of Onuf and Collins, seem to point with considerable unanimity to the intermedio- 

 lateral tract as being the source of the sympathetic fibres. It must be admitted, 

 however, that other observers have found conflicting, and sometimes unintelligible, 

 TRANS. ROY. SOC. EDIN., VOL. XLV. PART I. (NO. 5). 17 



