Turner, Morp/ioloi^y of t/w Avian Brain. 131 



to the vicinity of the chiasm. It then turns cephalo-mesad 

 and decussates in the cephalo-ventral part of the dien- 

 cephalon. 



Dorso-median fasciciilits (Plate XIV, Fig. 12). — This 

 bundle passes between the roots of the fourth and third 

 nerves. It w^ill be more fully described in a subsequent 

 paper. 



Pyrauiidal tracts. — In the first paper of this series all 

 tracts, excepting the tractus Bummi, passing from the dien- 

 cephalon to the prosencephalon were included under this 

 name. Here this name is restricted to the crossed and the 

 direct pyramidal tracts of the cord. In the lateral portion 

 of the diencephalon these tracts pass along the ventral sur- 

 face of the brain, slightly dorsad to the chiasm. Cephalad 

 to the crura cerebri they curve laterad into the prosen- 

 cephalon. 



PLATE XIV. 



Figs. 1-G. Transverse sections of the diencephalon and mesen- 

 cephalon oi Sialia .'iialis. F. /., fasciculus internus; A., mesencephalic 

 tract of the third nerve; C. P., corpus posterius; JV. /,., nidulus lenticu- 

 laris; JV. P., nidulus pjriformis; O. C, commissura Sylvii; P. C, pos- 

 terior commissure; P. A^., peduncular nidulus; 6". C, superior com- 

 missure; ///, root of third nerve; /F, root of fovirth nerve. 



Figs. 7-9. Horizontal longitudinal sections of the caudad portion of 

 the brain of a chicken. A. P., anterior peduncle of epencephalon; 

 D. M. F., dorso-median fascicvilus; A/. O. T., median optic bundle; 

 O. C, commissura Sylvii; P. C, posterior commissure; P. JV., pedun- 

 cular nidulus; 5. C, superior commissure; ///, root of third nerve; 

 /// )/, nidulus of third nerve; /f', root of fourth nerve; IV n, nidulus 

 of fourth nerve. 



Fig. 10. Horizontal longitudinal section of a portion of the brain 

 oi Hylocic/ila s-^'aii/.^oiii. ^-t, tract passing from the mesencephalon to 

 a nidulus in the medulla; /f, root of fourth nerve. 



Fig. 11. Horizontal longitudinal section of the diencephalon of 

 Columba livia, taken near the ventral surface. D. /., decussatio infe- 

 rior; F. A., fibr:e ansulata;; O. C, optic chiasm. 



Fig. 1£. Longitudinal-perpendicular section of Sia/ia sialis, taken 

 through the root of the third nerve. I). 3/. 7^., dorso-median fasciculus; 

 ///, root of third nerve; /f ;/, nidulus of third nerve. 



Fig. 13. Horizontal longitudinal section through a portion of the 



