18 The Structure of the Spinal Cord of the Ostrich 



the substantia gelatinosa centralis, in the middle of the grey commis- 

 sure. Where the grey commissure is lacking, in the region of the sinus 

 rhomboideus, the central canal is supported just dorsal to the commissura 

 ventralis by the loose strands of glial fibres which bridge over the space 

 between the blunt ends of grey substance. 



The lumen of the canal varies in irregular manner from round to oval, 

 and Avhere it lacks the support of the grey commissure it is no more than 

 a narrow slit. Where it is round or oval it has a diameter averaging from 

 .035 to .04 mm. In both cross and longitudinal stained preparations 

 there is seen within the lumen the so-called Rcissner'sche C entralfaden. 

 Kolliker " in a recent contribution gives the opinion that it is a " natiir- 

 liche Bildung beim Vogel, Eeptilien, und Amphibia," and also finds in it 

 " eine iiberraschende Aehnlichkeit mit einem Achsencylinder." This is 

 contrary to Gadoiv " who considers it a product of shrunken cerebro-spinal 

 fluid and lymph corpuscles. In favor of the view as held by Gadow may 

 be stated the three following facts : The structure shows a marked and 

 irregular variation in form and size in different sections; in some trans- 

 verse sections it was seen as multiple " Centralfaden " ; in sections 

 stained with toluidin blue it retains a deep blue stain while the axis-cylin- 

 ders in all other parts of the section are unstained. 



Xerve-Cell Groups. 



The, majority of the nerve-cells of the spinal cord of the ostrich are 

 situated in the grey matter of the ventral horn. There are, however, 

 many cells in the grey commissure and the dorsal horn, and there are 

 still other cells among the fibres of the white substance, especialty near 

 the periphery. These cells vary at different levels in their form, size, and 

 manner of grouping. For their descriptions the following classification 

 has been found advantageous: 



1. Lateral Group — a. Lateral cells. 



b. Dorso-lateral cells. 



c. Ventro-lateral cells. 



2. Central Group — a. Small mixed cells. 



b. Giant cells. 



3. Commissural Group— 



i 4. Dorsal Group — a. Clarke cells. 



b. Dorsal horn-cells. 

 5. Peripheral Group — a. Nuclei marginales majores. 



b. Nuclei marginales minores. 



c. Scattered cells. 



" Kolliker, L. c, p. 159. 

 " Gadow, L. c, p. 338. 



