154 TEIJI HOSHINO 



marked in the anterior portion. The fibers from the reticular 

 formation to the peduncle are hardly recognizable. 



In the medulla oblongata, the most conspicuous and constant 

 changes in all affected birds are the reduction of the fiber bundles 

 in the ventral periphery of the brain stem, the fasciculus longi- 

 tudinalis medialis, the cerebellar peduncle, and the reticular 

 formation, including the internal arcuate fibers and ganglion 

 cells. Other differences, though not so considerable as in the 

 above structures, and sometimes not constant, may be pointed out : 

 the reduction of the nuclei funiculi posteriores, nucleus olivaris 

 inferior with its inter- and circumolivary fibers, and a sym- 

 metrical nucleus which is located at the ventral periphery in the 

 middle portion of the brain stem. All the cranial nerves are nor- 

 mal in nuclei and fibers in all affected birds. The nucleus ruber, 

 the brachium conjunctivum, the nucleus isthmi (nucleus lemniscus 

 lateralis) in the midbrain, and the nucleus mesencephalicus lat- 

 eralis in the optic lobe appear in good condition. 



In addition to the small size of the gray and white matter in 

 the spinal cord en masse, there is decidedly poor developmen of 

 cells in Clarke's column, the anterior horn, and the central gray 

 matter, all those present being small in size, often one-half the 

 normal, few in number, with scanty processes. The median 

 portion of the funiculus anterior, the direct spinocerebellar tract, 

 and the posterior funiculi are reduced in area and also show indis- 

 tinct borders owing to the intermingling of abnormally small and 

 delicate fibers which show a diminution of caliber. The fiber 

 network in all the gray matter, especially, in Clarke's column is 

 scant. The capillaries and small blood-vessels in the substance 

 of the spinal cord and cerebellar cortex are apparently greatly 

 reduced. None of the spinal roots or Lissauer's zone show any 

 variations. In all cases there is never seen a definite degenera- 

 tive or regressive process, such as segmentation of myelin sheaths, 

 or increases of the neuroglia or interstitial tissues. No thicken- 

 ing of the pia mater, the coats of the blood-vessels, or abnormal 

 cell infiltration is observed. 



Thus, the changes in the central nervous system in the affected 

 pigeons may be regarded as a hypoplasia or developmental inhi- 



