Ti'RNEK, MorpJiology of tJic Avian Brain. z'^ i 



densely stained nucleolus. From the proximal extremity of 

 each cell a nerve fibre passes into the metencephalon, while 

 from the distal extremity of the same cell a nerve fibre passes 

 into the nerve. 



Nidiilus of the Abducens Nerve (Plate XVIII, Fig. lo, 13). 

 — This is an ill-defined nidulus which lies hear the meson 

 and which extends as far cephalad as the external root of the 

 sixth nerve. In the alligator brain(') and in the human 

 brain(^) this cell cluster is situated on the floor of the fourth 

 ventricle. In the avian brain, however, this nidulus is not 

 adjacent to the ventricle, but is separated from it by a large 

 faciculus of nerve fibres. 



This nidulus is composed chiefly of rather small, irregular, 

 pyramidal cells, which resemble those of the niduli of the 

 oculo-motor and pathetic nerves. True, these cells are more 

 irregular than those figured in Plate XVI, Figs. 13, 14; but 

 the cells of the niduli of the third and fourth nerves also are 

 usually more irregular than the cells there delineated. In 

 hasmatoxylin and in alumininium-sulphate cochineal prepa- 

 rations, these cells are usually densely stained, and each cell 

 presents a small densely stained nucleus, within which is a 

 densely stained nucleolus. This nidulus is well supplied 

 with Deiter's corpuscles. 



Niduli of the Facial and of the Auditory Nerves (Plate 

 XVIII, Figs. 3, 4, II, 13, 18). — Since in the avian brain the 

 seventh and eighth nerves have a common root, it has been 

 thought wise to describe the niduli pertaining to that root as 

 though they were the niduli of a single mixed nerve. In the 

 avian metencephalon at least three distinct niduli are related 

 to the fibres of facial and auditory nerves. For convenience 

 these are here designated as " nidulus L," " nidulus B," 

 " nidulus Y." 



Nidulus L (Plate XVIII, Fig. 18).— Far laterad,near the 

 the root of the auditory nerve, there is a small sub-spherical 



1 Prof. C. L. Herrick, op. cit., p. 153. 



2 Prof. Ambrose L. Rannev, op. cit., p, 339. 



