HISTOLOGY OF SENSORY GANGLIA OF BIRDS 265 



average minor diameter 21 ^i, while those of small size, including 

 80 per cent of the cells, had an average major diameter of 14.5 n 

 and an average minor diameter of 12.5 m- 



2. , Cerebral ganglia 



a. The vagus ganglion. In the screech owl this ganglion is 

 slightly smaller than the Gasserian. Near the periphery the 

 cells are compactly arranged, but at the center are distributed in 

 clustiers that are separated by bundles of nerve fibers and connec- 

 tive tissue. 



In the vagus ganglion of the owl the largest cell observed was 

 41 /x long and 33 broad, and the smallest one 18 by 17 At. The 

 average size is about 32 ix long and 27 wide. The majority of the 

 cells are rounded in outline, the cells with the major diameter 

 much greater than the minor diameter being few in number. 

 There are also lobulated cells, ranging from mere superficial 

 irregularities to deep indentations forming distinct lobes (fig. 

 25). Figure 27 {lb.) shows a lobe of intermediate size. 



The nuclei are very regular, with clearly defined outline. 

 They are round to elliptical in shape but the rounded ones are 

 much more numerous than the elliptical. The elliptically shaped 

 nuclei are found in the cells that have considerable difference 

 between their major and minor diameters. Only one nucleolus 

 was observed in any one nucleus. 



In cells of vagus and Gasserian twists and turns of the main 

 process are common (figs. 29, 30, 32), and occasionally a simple 

 glomerulus was seen (fig. 25, vagus; fig. 33, Gasserian). 



Accessory processes arising from the main process near its 

 junction with the cell are of frequent occurrence. These processes 

 usually end in small rounded enlargements, but in some cases 

 they end without enlargements. Figures 28 and 29 show minute 

 accessory processes terminating in bulbs, while figure 25 shows 

 accessory processes without and one with the enlarged termina- 

 tion. All the accessory processes observed (except ac.pr., in 

 fig. 30) terminated within the capsule. 



