TuKNYLK^ M^orphology of the Aviafz Brain. z8i 



tance cephalad of the trochlear niduhis the major portion of 

 this fasciculus turns and passes obliquely to the ventral sur- 

 face of the medulla, thence into the myelon. A few fibres, 

 however, continue caudad and remain near the dorsal surface 

 of the metencephalon. Throughout its course this tract con- 

 tinues near the meson. Although it has not been possible to 

 trace fibres from this fasciculus into any of the niduli of the 

 avian medulla, yet it is evident that fibres are given off' all 

 along the line. Although the evidence at hand is not quite 

 conclusive, yet I am inclined to believe the relationship of 

 the avian posterior longitudinal fasciculus is the same as that 

 described above by Edinger for the human posterior longitu- 

 dinal fasciculus. 



Fibres Arcuatce (Plate XVIII, Fig. 14). — On a level with 

 the auditory nidulus a convex tract, with its convexity pro- 

 jecting laterad, passes from a nidulus in the peduncle of 

 the epencephalon to a nidulus in the ventral portion of the 

 metencephalon. 



CONCLUDIN(; REMARKS. 



I. Economy of space is evidenced in all parts of the avian 

 brain, and the phrase " higher type of birds" carries with it 

 the significance " greater compactness of the brain." Indeed, 

 progressive compactness has played so important a part in 

 the evolution of birds that there is a vast difterence between 

 the lowest avian brains, with their large projecting olfactory 

 lobes and exposed optic lobes, and the highest avian brains, 

 with their small, inconspicuous olfactory lobes and covered 

 optic lobes. The difference between these two extremes is 

 almost as great as that between the brain of the lizard and 

 the brain of the lower types of birds. Yet there is no im- 

 passable gulf between the brains of the lowest and the brains 

 of the highest types of birds, for all the intervening stages 

 are supplied by the brains of the various avian groups. In 

 reviewing this remarkable sequence, we are almost forced to 

 believe that this tendency towards compactness of the brain 



