BRAINS AND SPINAL CORDS IN ATAXIC PIGEONS 129 



the funiculus proprius anterior in the normal, but in the affected 

 birds, it does not protrude or is quite indefinite and contains 

 fewer and smaller cells. Fibers which run in the anterior horn 

 are few, especially those which run toward the central gray 

 matter. 



The nerve cells in the base of the posterior horn with their 

 fiber network are changed strikingly, about which further 

 description will be given later under the title of Clarke's column. 



The dorsal horn shows a marked reduction in its breadth in all 

 the pigeons, especially at its base, notwithstanding the fact that 

 it is almost as long as the normal. 



In the normal specimen, at the enlargements, especially in the 

 lower, there are usually a few large polygonal ganglion cells 22.8 n 

 on the average at the lateral border of the central gray matter, 

 and sometimes they are even in the reticular formation of the 

 lateral funiculus near the border. These cells are rarely found 

 in the affected birds or, if present, are small and few in number. 

 The anterior commissure which connects both halves of the cord 

 at the level of the lower enlargement is scant, and consequently 

 the fibers running into the anterior horn and central gray matter 

 seem to be very few in number. 



The column of Clarke. In the spinal cord of the pigeon, es- 

 pecially at the level of the upper and lower enlargements, we find 

 a large group of ganglion cells with an interlacement of fiber retic- 

 ulum at the base of the dorsal horn, symmetrically located and 

 adjoining the funiculus posterior. This structure corresponds to 

 the so-called Clarke's column in the thoracic cord of mammals. 

 It may be well to describe a little more thoroughly this column 

 of cells in the normal pigeon's cord, for only a few observations 

 have been hitherto made on this structure in pigeons and other 

 birds. 



In the cervical region above the upper enlargement, there can 

 hardly be found a well-developed structure analogous to this 

 column; the narrow H-shaped gray matter exhibits no marked 

 thickening at the base of the posterior horns. Only a few small 

 round cells 5.7 to 7.1 fj. in diameter not well defined from the 

 cells in the central gray substance are visible, and the network 



