28 ATLAS OF NERVE CELLS 



The posterior horn of the spinal cord presents a peculiar structure differing from that 

 of the remainder of the gray matter. This is evident in Plates I. and II. and is more 

 clearly shown in Plate X. It has a peripheral portion and a central portion. The 

 peripheral portion is known as the substance of Rolando, and about its posterior part is a 

 zone of somewhat different appearance known as the spongy layer. The substance of 

 Rolando extends through the entire length of the cord and upward through the medulla 

 and pons, being there in close relation with the termination of the sensory branches of the 

 fifth nerve. It appears, therefore, to have a sensory function. This substance resists many 

 staining materials, and it is only within a short time that its actual structure has been 

 determined by Cajal and Lenhossek. It has a granular homogenous appearance, but they 

 have found that it contains many very small polygonal cells, with dendrites and a neuraxon, 

 the latter coming off from the dorsal side and passing into the lateral column of the cord, 

 where it divides and passes up and down as do the other longitudinal fibres of the cord. 

 About these cells there is a mass of interlacing fibres of most minute calibre, too fine to 

 be stained by ordinary methods. 



In the spongy zone, outside the Rolandic substance, lie much larger cells, whose long 

 axis is parallel with the periphery of the cord, and whose dendrites and neuraxons enter the 

 posterior and lateral columns. 



The central portion of the posterior horn is made up of a coarser mesh of fibres and 

 of numerous posterior nerve root fibres which traverse it to reach the central gray matter. 

 It contains many of the intrinsic cells already described. 



Plate X. shows the entire posterior horn of the cord, including both the substance of 

 Rolando and the spongy zone. The large cell seen near the surface of the cord (at the 

 bottom of the plate), whose long axis is parallel with the surface of the cord, and which 

 has numerous processes passing both into the posterior and lateral columns, and directly into 

 the posterior horn, is the type of cell described by Cajal, and known as the border cell. 

 These cells are supposed to be association cells, and their neuraxon appears to pass uniformly 

 into the posterior columns. The general homogenous structure of the substance of Rolando 

 appears in the plate, but it is seen to be traversed by numerous fibres, which enter the 

 posterior horn from the posterior nerve root. These pass directly to the plexus of nerve 

 fibres which lies deep within the horn near to its base. 



