400 ANATOMY AND PHYSIOLOGY OF THE SPINAL CORD. 



merely the nearest of the longitudinal turned inward to 

 gain the ganglionic cells ; others consist of fibres passing 

 across the inferior or white commissure, which is entirely 

 made up of such decussating fibres ; a third class are the 

 fibres which form the roots of the motor nerves passing 

 outward, usually in two bundles, toward the surface of the 

 cord. 



The anterior horns of grey matter contain superficially a 

 number of marginal or circumferential fibres intermixed with 

 small ganglionic cells. These fibres, which are derived from 

 those of the column, are connected with the cells, and these 

 in turn with larger ganglionic cells placed in the middle 

 and anterior part of the horn. The large cells are arranged 

 in groups, and each group, according to Van der Kolk, 

 represents and presides over a muscle or a group of muscles, 

 which act always in concert. These cells are multipolar, 

 the prolongations going some to connect them with super- 

 ficial small cells, or directly through the longitudinal fibres 

 of the anterior column with the brain ; some to the adjacent 

 cells of the same group ; some to join the cells in the 

 posterior horn of grey matter ; and others to form the roots 

 of the motor nerves. 



The posterior columns are, like the anterior, made up of 

 (1.) longitudinal fibres externally, which become oblique 

 internally before they pass into the grey, and (2.) of trans- 

 verse fibres, which, passing outward from the grey matter, 

 form plexuses amongst the longitudinal. Some of the 

 longitudinal fibres are continuous with fibres of the superior 

 roots of the nerves, which accordingly proceed directly to 

 the brain without entering the grey matter : these are the 

 sensitive fibres. The transverse fibres seem, on the other 

 hand, to be the reflex roots. These latter pass through the 

 substance of the superior grey horn to join some groups of 



