54 BULLETIN OF THE LABORATORIES 



columns to be quite different in having much larger fibres with a con- 

 siderable amount of surrounding neuroglia. 



The ventral root-zone is represented in Plate XIII, Fig. 2, and is 

 found to spread out over the greater part of the lateral aspect of the 

 cord. The ventral root does not leave the cord as a distinct bundle, 

 as is the case with the dorsal root, but is formed from an extension of 

 the fibres from the whole side of the ventral cornu, which radiate to 

 the surface of the cord and then converge to the ventral root. 



The dorsal root enters as a large bundle. Part of its fibres pass 

 into the dorsal root-zone or Burdach's columns and part pass directly 

 into the dorsal cornu and there enter the cells of the gray matter, while 

 part pass directly to the opposite side through the posterior commis- 

 sure. 



The distribution of the gray matter is essentially the same as that 

 of the rabbit. The ventral cornu is rather broad but very short and 

 contains two groups of multipolar cells. One median grou]) (Plate 

 XIII, Fio. I, (7, Fig. 3, Fig. 4, /», and Fig. 8,) is situated at the median 

 angle of the cornu, having cells from .015 to .02 mm. in transverse 

 diameter. These cells send off processes to the ventral columns, which 

 eventually pass into the ventral roots, also processes which seem to 

 pass to the dorsal cornu, and some which pass through the ventral com- 

 missure to the opposite side. 



The other cell group (Plate XIII, Fig. 4 <:, Fig. 9,) is situated 

 external to the first and forms a lateral nucleus The cells resemble 

 those of the median group very closely and send their processes in the 

 same directions. 



The cells of the gray matter of the dorsal cornu are much smaller 

 than those of the ventral. They occur in greatest numbers in the cer- 

 vix of the cornu (Plate XIII, Fig. i, b, Fig. 2, Fig. 4, a, Fig. 5.) 

 These cells are from .005 to .01 mm. in transverse diameter and are 

 multipolar in form. The processes to which they give origin follow 

 the direction of the fibres in which the cells are imbedded, but whether 

 they are simply the nodal points of these fibres and do not represent 

 true cells may be questioned. They are nucleated and, except in size, 

 resemble very closely the motor cells of the anterior cornu. Besides 

 these distinct cell groups there are also numerous cells scattered 

 rather irregularly throughout the gray mass, and at the exits of 

 the ventral roots. These cells, which lie lateral to the central canal, 

 increase greatly in number and size and appear to form a large nucleus 



