BRAINS AND SPINAL CORDS IN ATAXIC PIGEONS 147 



cerebellar peduncle dorsally. These fibers can be easily seen in 

 the normal section, while in the affected section they cannot be 

 seen distinctly at all. The area and staining properties of the 

 spinal root of the nervus trigeminus are normal. In the ventral 

 region of the cerebellar peduncle, more proximally than the 

 acoustic area and the vestibular fibers, there appears a large 

 oval nucleus, with the long axis from the mediodorsal to the 

 ventrolateral portion of the brain stem. This is the sensory 

 nucleus of the trigeminal nerve (nucleus magnus nervi trigemini, 

 Wallenberg). In the lateral area of this nucleus there runs a 

 thick bundle from the brain stem laterally to the cerebellar pe- 

 duncle, but there are also fiber groups which run to the medial 

 side of the cerebellum. The fiber bundles which surround this 

 nucleus at its medial side run chiefly to the medial region of the 

 cerebellar body, some of them, however, cross in the midline at 

 the base of the cerebellar body. From the sensory nucleus of 

 the trigeminal nerve fibers emerge at its ventrolateral border and 

 pass out of the brain sterm 



The nucleus with its contained cells as well as its peripheral 

 fibers when compared with the normal reveals no abnormalities. 



The three nuclei of the motor V. described by Brandis ('95) 

 with their cells and fibers appear perfectly normal. 



The fasc. long. med. and external ventral arcuate fiber bundle 

 in all affected specimens are less well developed as at the former 

 level. The eminences of the fasc. long. med. in the floor of the 

 fourth ventricle are much flatter than normal. In pigeon no. 

 K207, the fiber bundle at the ventral periphery of the brain stem 

 is almost absent. 



At the ventral part of the brain stem there is a symmetrical 

 small nucleus, directly dorsal to the external ventral arcuate 

 bundle. This nucleus lies medial to the intracerebral roots of 

 the nervus abducens; it is round in shape and contains about 

 eighteen small round cells. Surrounding this nucleus there are 

 some fibers which cross the raphe tranversely to the other nu- 

 cleus. In the ataxic specimens except pigeon no. K172, this 

 nucleus is rather flat than round, contains smaller and fewer cells 

 and the interspersed fibers are few; the fibers around it are ap- 



