BRAINS AND SPINAL CORDS IN ATAXIC PIGEONS 149 



edge of the medulla oblongata which hitherto ran longitudinally, 

 changes its direction dorsalward. As one goes cerebralward, 

 the peduncle increases in its thickness, gathering fibers from the 

 medulla oblongata. When the wide bundle of the nervus vestib- 

 ularis appears, one sees a large fiber mass running dorsally from 

 the lateral edge of the medulla oblongata to the lateral portion 

 of the cerebellar peduncle whose fibers go chiefly to the cortex 

 on the same side. This fiber mass gradually increases in breadth, 

 receiving fibers from a bundle which runs on the ventral periph- 

 ery of the medulla oblongata from one side of the cerebellar 

 peduncle to the other. This ventral fiber bundle shows its maxi- 

 mal thickness at the level where the cerebellar peduncle has its 

 greatest thickness, i.e., at the proximal portion of the vestibu- 

 lar nerve. Regarding this fiber bundle, from its relation to the 

 cerebellum, from its anatomical localization, and especially from 

 its striking diminution in size (one-third to one-half the normal 

 breadth in all the affected birds), it will not be a great mistake 

 to indorse Stieda, who suggests that this fiber bundle in large 

 part, if not wholly, is comparable with the pons varolii of 

 mammals. 



At the region where the facial nerve fibers appear in the 

 medulla and the nucleus cerebellaris medialis forms a large round 

 nucleus in the cerebellum, the fibers in the peduncle become 

 more and more numerous, and go not only to the lateral portion, 

 but also to the median portion of the cerebellar body, some of 

 them crossing the midline to the opposite side. The fibers of 

 the brachium conjunctivum appear at the medial edge of the 

 peduncle. Then at the ventrolateral base of the peduncle, tak- 

 ing the place of the position of the large cell area of the acoustic 

 field, the oval sensory nucleus of the trigeminal nerve appears, 

 well surrounded by medullated fibers, as indicated before. We 

 see here nothing but a rich mass of fibers in the peduncle which 

 run to the lateral and medial parts of the cerebellar body. Far- 

 ther proximally, the fibers which go from the dorsal portion of 

 the brain stem into the velum medullare appear. At the location 

 where the massive bundle of the sensory V. root appears, the 

 connection between the cerebellum and brain stem is lost. After 



