CONNECTION OF NERVE-CELLS WITH FIBRES. 51 



cells far enough to establish beyond doubt their exact rela- 

 tions. 



These two considerations alone are sufficient to account 

 for the uncertainty so apparent even in the most successful 

 investigations into the anatomy of the central nervous sys- 

 tem ; and we shall content ourselves, in view of these facts, 

 with giving a summary of what seems to be the probable 

 relation of the cells to the fibres of origin of the nerves and 

 to each other. 



Apolar cells, if they exist at all and be not cells from 

 which the poles have become separated, are simple, rounded 

 bodies, lying between the fibres, with which they have no 

 other relation than that of mere contiguity. Unipolar cells 

 have but one prolongation, which is continuous with a 

 nerve-fibre. It is not certain that these exist in the human 

 subject. 



Bipolar cells are found in the ganglia of the posterior 

 roots of the spinal nerves and some of the sympathetic gan- 

 glia. In many of the lower animals, particularly in fishes, 

 the cells of the ganglia of the spinal nerves are simple, nucle- 

 ated enlargements in the course of the sensitive nerve-fibres, 

 and many anatomists have inferred that the same arrange- 

 ment exists in man and the mammalia ; x but the constitution 

 of these ganglia in the higher classes of animals seems to be 

 entirely different. In the first place, the roots of the spinal 

 nerves at the ganglia are undoubtedly reenforced by the ad- 

 dition of new fibres, as Kolliker has shown by actual meas- 

 urement, the roots being sensibly larger beyond the ganglia 

 while the filaments of entrance and exit have the same diam- 

 eter. 3 Direct observation upon the ganglia in man also fails 

 to show the arrangement so clearly demonstrable in fishes. 

 The cells in the posterior roots are not continuous with the 

 fibres passing from the periphery to the cord, but give origin 

 to new fibres, generally two in number, which sometimes are* 



1 LONGET, Traite de physiologic, Paris, 1869, tome iii., p. 95. 

 * KOLLIKER, Elements d'histologie humaine, Paris, 1868, p. 419. 



