THE COUBSE OF THE FIBEES IN THE SPINAL COED. 359 



In the fetus of different mammals different dispositions of fibers have been 

 found in this commissure, according to the class of animal examined. In the dog, 

 for example, three divisions of these commissural fibers can be distinguished; in the 

 cow only two, and so forth. 



As far as the anatomic relations of the component tracts of the spinal cord 

 could be determined macroscopically, Burdach, Sommering, and J. Arnold rendered 

 important service. Bellingeri was the first to recognize the connection between the 

 gray mattei- of the ventral horns and the anterior nerve-roots; Grainger, that be- 

 tween the dorsal horns and the posterior nerve-roots. The minute structure of the 

 cord was first revealed by B. Stilling, later Kolliker, Goll, Deiters, Gerlach, Clarke, 

 and others have added to our knowledge of it. To the labors of Tiirck, Fleohsig, 

 Charcot, and Gowers we are indebted for the major part of our ideas of the dis- 

 position of the fibers of the white matter. Within more recent times, however, 

 through the advances made by His, Golgi, and S. RamOn y Cajal (collaterals, arbor- 

 ization of axis-cylinders, etc.), through the researches of KiSUiker, Van Gehuehten, 

 and Lenhossek, of whom mention has already been made in the introductory chapter, 

 a very important gain has been made in our knowledge of the spinal cord. Besides 

 them. Singer and Munzer, Lowenthal, Mott, and others have cleared up much that 

 was not understood, and we are indebted to Waldeyer for a critical revision of 

 accumiilated data, together with many new subjects. 



One might carry the study of the most important fiber-systems in the 

 cord much farther, going into many interesting details. But we have already 

 found so many places where uncertainty prevails that, adhering strictly to 

 the limits, beyond which one finds only a complex of details and contra- 

 dictory opinions of authors, we need hardly pursue it farther. 



In the introduction to his great work on the structure of the spinal 

 cord. Stilling says: "We must not forget, following in the train of the noble 

 Burdach, that in the examination of the spinal cord we are exploring a 

 wonderland, which we know very little about; and we may only gaze at the 

 rivers and mountains, to get a clear general understanding of the whole, 

 leaving to our successors to explore every brook and to seek out every 

 height." 



Thirty-six years have passed since, with these prefatory words, one of 

 the most valuable books appeared with which the anatomic department of 

 science has been enriched, and to-day we are still far from the goal; it will 

 be long still before that field-map will be completed, of which Burdach and 

 Stilling dreamed. 



In the cord there lie in close proximity to each other, physiologically widely 

 differentiated fibers; the cells, which may be regarded as central cells, are thickly 

 surrounded by peripheral conducting paths. It is clear from this that it is very 

 difficult to learn the results and to establish the symptoms which appear upon dis- 

 ease or lesion of any of these component parts of the cord. 



Still, close observations at the sick-bed and at autopsies have taught much 

 in this connection. A number of spinal-cord diseases affect invariably certain por- 

 tions of the cord, always certain tracts or particular groups of ganglion-cells, and 

 leave the other tracts of the cross-section intact, forever or for a long time. The 



