HISTOLOGY OF SENSORY GANGLIA OF BIRDS 259 



exhibiting stages between the oppositi-polar and the unipolar 

 (figs 12, 6i; 62). Implantation cones were infrequent. 



h. The vagus ganglion. The ganglion of the tenth nerve is so 

 encased in bone that it is difficult to remove it without injury. 

 This large, complex ganglion is, in the adult fowl, about 2 mm. 

 long by 1.25 mm. broad, and it must be looked upon as the product 

 of the union of several ganglia. The roots of the glossopharyn- 

 geal run through the vagus. Sections of the vagus, embracing 

 also the roots of the ninth nerve, show cells in that part through 

 which the fibers of the ninth run, but it was impossible to deter- 

 mine whether any of these cells send fibers into the ninth nerve. 

 The cells are more numerous around the periphery than in the 

 center of the ganglion where they are separated into elongated 

 groups by bundles of fibers. At the proximal end the large num- 

 ber of fibers passing into the numerous roots give to this part of 

 the ganglion a characteristic appearance. 



■ In the vagus ganglion there is considerable range in the size 

 of the cells (fig. 13, h and c), the major diameters varying between 

 18 and 74 /x and the minor between 15 and 40 yu, those of medium 

 size predominating. Cells of unusual length are generally narrow. 

 The shape of the cells differs as in the other ganglia, round, ellip- 

 tical, and pear-shaped being common while a small number are 

 club-shaped. The nuclei are round to oval, the rounded ones 

 being from 6 to 1 1 ju in diameter and the oval ones between 6 and 

 16 m ii^ length. A single nucleolus located near the center was 

 observed in each nucleus. 



As in the other ganglia the prevailing type of cell is unipolar. 

 There were a few bipolar cells showing gradations between oppo- 

 siti-polar and unipolar. In a careful count of ten conservative 

 sections of a vagus ganglion of a six-year-old hen were found 481 

 unipolar cells and only 2 bipolar; 57 of the cells showed pericellular 

 networks, 5 of them had accessory processes and 3 showed fenes- 

 trations. In two other sections of the same ganglion, out of 114 

 unipolar cells, the processes of 101 issued from the distal end of the 

 cell and continued in a distal direction. In one instance only the 

 process issued from the proximal end, and the processes of the 

 remaining 12 cells emerged from the side of the cells. The major- 



