BRAINS AND SPINAL CORDS IN ATAXIC PIGEONS 131 



appears again in good development and almost equal to that in 

 the upper enlargement. Here in the lower enlargement the 

 structure is less distinct than in the upper, especially in its lateral 

 and ventral borders; its border adjacent to the central gray mat- 

 ter is somewhat diffcult to distinguish. In the sacral region 

 the typical columnal feature is lost, but there often remain one 

 or two large round or oval cells at the corresponding place. 



In the affected birds, at the level of the upper cervical cord, 

 the nerve cells in the base of the dorsal horn and in the central 

 gray matter are small and measure on the average 6.4 p., while 

 in the normal they measure 8.6 p. in size; they are also reduced in 

 number. The small size of the cells makes it hardly possible to 

 describe their internal structure, but the striking narrowness of 

 the posterior horn at its base must be remembered. In the upper 

 enlargement, Clarke's column, which is at its maximal thickness 

 at this level, has a decidedly small size, fewer cells and less reticu- 

 lum in all affected specimens. The cells have a spindle-like slender 

 shape and are rarely shrunken and are not at all like the large 

 round or oval normal cells. The fibers around and in the col- 

 umn are few, stain weaker, are thin and short, and often they 

 seem as if they were cut off in pieces. They run into the dorsal 

 horn from the funiculus dorsalis or from the dorsal roots, and in 

 the normal they may follow into the central gray matter or 

 reticular formation in the lateral funiculus, but in the affected 

 birds they are usually quite thin and show a short course. 



At the level of the lower enlargement, Clarke's column meas- 

 ures, though not exactly determined, about 0.317 to 0.384 mm. 

 in the normal and 0.200 to 0.251 mm. in the affected birds. The 

 cells in the affected sections are small and few in number, measur- 

 ing 14.2 /x in diameter. In the affected specimens these cells are 

 really quite rare, only one to three are found in a field at the most, 

 while in the normal three to five are found in one field, and these 

 measure 39.9 to 51.1 n in diameter. The cells in the affected 

 birds have usually a slender shape and sometimes, though rarely,, 

 seem to be slightly shrunken. Fibers which go from the end of 

 the posterior horn or into the central gray matter in the normal 

 take a path in a direction ventrolateral^ or transversely at the 



