494 SPECIAL HISTOLOGY. 



spinal nerves and of the sympathetic, and in the optic thalami, 

 both sorts of fibres arise, in one place, from small, and in another 

 from large cells. It seems, therefore, as in the case of the 

 nerve-fibres, that there are large and small motor cells, as well as 

 sensitive cells of various dimensions, a fact which is confirmed 

 by comparative anatomy, as the large bipolar cells in Fishes 

 are manifestly sensitive. No essential difference can be pointed 

 out between sensitive and motor cells, whether the latter be of 

 uniform or of different size, and in particular the variations ex- 

 isting between such cells are not greater than those between the 

 motor cells in different localities. Even the cells in the 

 cortical substance of the brain, to which Physiologists assign 

 the mental manifestations, with our present means of research, 

 exhibit no perceptible peculiarities. The nerve-cells, however, 

 may be divided into those which are in direct connection with 

 nerve-fibres, and those which are not thus connected, but in- 

 dependent. The former, of course, are to be especially regarded 

 as sensitive and motor, with respect to the latter, anatomy to 

 some extent affords no information, inasmuch as, that they 

 present no processes, as in the sympathetic ganglia, and in some 

 situations in the brain ; as regards those furnished with pro- 

 cesses, particularly the many- rayed cells, which in many situa- 

 tions undoubtedly are not prolonged into nerve-fibres, it might 

 be considered certain that they, — both larger and smaller, by 

 means of their processes which fulfil the functions of nerves, 

 and whether the latter anastomose or not, — bring different 

 regions of the central organs into mutual connection, and par- 

 ticipate in the reflex phenomena, the sympathies, and other 

 modes of association of the functions. Cells of this kind exist 

 in the spinal cord and brain everywhere in very large quantity, 

 but not in the ganglia, although it is not, from this, intended 

 to imply that no reflex actions are performed iu those bodies. 



Respecting the nerve-fibres, anatomy is not in a condition to 

 point out any difference in them, between the sensitive and 

 motor nerves ; a circumstance, however, which, physiologically, 

 can afford no reason to ascribe identical functions to them. 

 As regards the various sizes of the nerve-fibres, the numerous 

 changes in diameter, undergone in their course by all the 

 cerebro-spinal nerves, very obviously indicate that these pro- 

 portions have no relation to the functions of the fibres in 



