436 THE TISSUES. 



merely a conducting apparatus (p. 430) ; it must be inferred that 

 the cells are the source of motor impulses on the one hand, and 

 the recipients of sensory impressions on the other. 



It has been seen that the largest nerve-fibres are certainly mostly 

 motor, and the 'finest sensory and ganglionic. We also find the 

 largest nerve-cells in situations whence motor effects proceed: as in 

 the anterior horns of the spinal cord, among the fibres of the ante- 

 rior roots of the spinal nerves ; in the medulla oblongata, at the 

 points of origin of the motor cerebral nerves ; and in the cortical 

 substance of the cerebellum, pons Yarolii, and crura cerebri. On 

 the other hand, the smallest cells are found in the sensitive and 

 sympathetic regions as the posterior horns of the spinal cord, the 

 corpora restiformia, and quadrigemina; and in the sympathetic 

 ganglia. Still, there is no constant relation between the size of the 

 cells and their function, whether motor, sensory, or sympathetic; 

 since in the optic thalami and in the ganglia of the cerebro-spinal 

 nerves, and even of the sympathetic, both sorts of fibres arise, from 

 large cells in one place, and from small ones in another. There are, 

 however, more small cells in the sympathetic ganglia. 



But it must be remembered that many of the cells in the cere- 

 brum and the cord are probably neither motor, sympathetic, nor 

 sensory. Such are those which are not in direct connection, through 



Fig. 280. 



a. A large nerve-cell with diverging and branching processes, some of which (6) are seen to pass 

 off into extremely minute filaments. These hear a very close resemblance to the axis-cylinder 

 of a tubular fibre, e. Small nerve-cells. /. Small nerve-fibres, some being varicose. 



their processes, with the nerve-fibres. Of these there are two kinds : 

 ls, apolar cells, existing in the sympathetic ganglia, and in some 

 situations in the brain (Fig. 289) ; 2c%, multipolar cells (Fig. 280), 



