402 ANATOMY AND PHYSIOLOGY OF THE SPINAL CORD. 



ganglionic cells in their interior, and, through the prolonga- 

 tions of these, appear to be more or less directly connected 

 with the groups in the anterior horns. 



The superior grey horns are made up in great part of 

 fine longitudinal fibres, and, as they are five or six times 

 thicker in the cervical and lumbar bulbs than elsewhere, it 

 is inferred that the fibres do not extend to the brain, but 

 become connected, at these points especially, with the 

 roots of the motor nerves. This is supported by the fact 

 that it is in the -parts presided over by the above enlarge- 

 ments that reflex actions are most frequently and energeti- 

 cally effected. 



The centre of the superior horns presents the nerve-cells 

 already referred to, and their surface has marginal fibres 

 with smaller cells similar to those of the anterior horns. 

 The grey commissure is formed of white fibres ; these are 

 not, however, any more than those of the white commissure, 

 connected directly with any nerve-roots. They seem, in 

 part at least, to connect the ganglion cells which on the 

 different sides receive the reflex roots, and Van der Kolk 

 suggests that they may insure a co-ordinate movement of 

 the two sides of the body in reflex actions. 



The spinal cord is possessed of all the functions predi- 

 cated of nervous centres, being itself but an aggregation of 

 such structures. This simple reservation may be made, 

 that it cannot directly affect or be acted on by the mind. 

 It may be stated shortly, that the spinal cord (1.) receives 

 impressions from all parts of the trunk, and generates motor 

 power as a result of such impression (reflex action) ; (2.) 

 transmits sensitive impressions to the brain ; (3.) conducts 

 motor force from the brain to be distributed through the 

 corresponding nerves; (4.) harmonizes motor power, and 

 leads to a simultaneous and uniform action of muscles, 



