HISTOLOGY OF SENSORY GANGLIA OF BIRDS 279 



The cells of the smaller ganglia of the small birds are quite 

 crowded, while in the larger birds the cells of the smaller gan- 

 glia have considerably more room. 



The size of the ganglion cells are in a measure proportional to 

 the size of the bird. There is usually considerable variability of 

 size in the cells of each ganglion. 



In the brachial ganglia of both the owl and the mallard duck 

 the cells are divisible on the basis of size into two classes, large 

 and small, the larger cells being much less numerous. 



The larger nuclei are usually found in the larger cells. In the 

 small birds the nuclei are larger in proportion to the size of the 

 cell than in the large birds. 



The outline of ganglion cells of birds is usually rounded or 

 elliptical with a small percentage of pear-shaped, club-shaped 

 and irregular forms. The ganglion cells of old birds show more 

 irregularities than those of young birds. Lobulated cells are 

 common in the Gasserian and tenth ganglia of the owl and less 

 common in the same ganglia of the mallard duck. 



In adult birds the predominating type of ganglion cell is uni- 

 polar with branches of unequal size from the main axis — a larger 

 branch going to the periphery and a small one to the central 

 nervous system. 



In embryos the ganglion cells are bipolar, beginning as oppo- 

 siti-polar and exhibiting gradations up to the unipolar condition. 

 In chick embryos of twelve to fourteen days incubation many 

 intermediate forms are present. 



Initial glomeruli and implantation cones are infrequent, except 

 in the Gasserian and the tenth ganglia of the owl. 



A remarkable coiling of the central axis of the peripheral 

 process was observed in the Gasserian ganglion of the chick, the 

 sheath not being affected. 



The ganglion cells of the old hen are less plump than those of 

 younger fowls and show many vacuoles. They also have a larger 

 number of protoplasmic slings and fenestrations. Complicated 

 fenestrations are present in the Gasserian ganglion of the old hen. 

 Simple fenestrations were seen in the same ganglion of young 

 birds. 



