252 E, VICTOR SMITH 



F. Sensory ganglia of the pigeon 275 



1 . Spinal ganglia 275 



2. Cerebral ganglia 276 



a. Ganglion of the ninth nerve 276 



b. The vagus ganglion '. . . . 276 



c. ' The Gasserian ganglion 277 



G. Sensory ganglia of the sparrow 277 



I. Spinal ganglia 277 



IV. Summary 278 



Bibliography 280 



I. INTRODUCTION 



The introduction of the modified silver reduction method of 

 Cajal ('05) gave a new impulse to the study of the structure of 

 the sensory ganglia. In these investigations, however, the gan- 

 glia of birds have received scant attention. Moreover, the obser- 

 vations have been confined chiefly to the spinal ganglia, with 

 occasional references to the Gasserian, and scarcely any study of 

 the remaining cerebral ganglia. It was with a view of supplying 

 a more comprehensive histological analysis of the sensory ganglia 

 of birds that this investigation was undertaken. The observa- 

 tions were carried on during 1909-10 and 1910-11 in the Zoologi- 

 cal Laboratory of Northwestern University under the direction 

 of Prof. William A. Locy, to whom grateful acknowledgment is 

 accorded for assistance and supervision. 



II. BRIEF COMMENTS ON THE LITERATURE 



The more important steps in the development of knowledge 

 regarding the nerve cells of the sensory ganglia may be summarily 

 stated. 2 After the pioneer observation (Ehrenberg '33, KoUiker 

 '44, etc.) came the recognition that the typical ganglion cell of 

 adult vertebrates above the fishes, consists of a cell body with a 

 main process that divides into two unequal branches, one going 

 centrally and the other peripherally. Further studies showed 

 that this typical form is produced by modifications of the oppositi- 

 polar cells of embrj^onic stages, and soon a whole series of transi- 



^ The pertinent literature (see bibliographical list) dealing with the histology 

 of the sensory ganglia of all classes of vertebrates was read and considered, but 

 would require too much space for a detailed review. 



