432 SPECIAL HISTOLOGY. 



as in the anterior horns of the spinal cord, amongst the fibres of the 

 anterior roots, in the medulla oblongata, at the points of origin of the 

 motor cerebral nerves, in the cortical substance of the cerebellum, the 

 23ons Va7'olii and crura cerebri; whilst the smallest cells are found in the 

 sensitive regions, as in the posterior horns of the spinal cord, the corpora 

 restiformia, and quadrigemina. There does not, however, appear to be 

 any constant relation between the size of the cells and the existence of 

 sensitive or motor functions, for, in the ganglia of the cerebro-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 difi'erent size, and in particular the variations existing 

 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 independent. 

 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 sym- 

 pathetic ganglia, and in some situations in the brain ; as regards those 

 furnished with processes, particularly the many-rayed cells, which in 

 many situations 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 participate 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 in 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 cir- 

 cumstance, 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 proportions have no relation to the functions of the fibres in gene- 

 ral. Nevertheless, I do not look upon these relations of size as alto- 



