Saroent. — Oiitic Reliex Apparatus. 



PLATE 7. 



Figs. 47-52 are parasagittal sections, anterior at the left, of the anterior roof of 

 mesencephalon, and torus longitiulinalis, cutting tlie posterior com- 

 missure, and sliowing something of the mode of formation of Keiss- 

 ner's fibre in tlie ventricle. Some details of tlie branches of the fibre 

 have been drawn in from adjacent sections. 



Ameiurus nebulosus, young, 4 cm. long. The midbrain roof is of the 

 primitive ganoid type. (Compare Figs. 25, 20, Date 4.) X 205. 



Notropis cornutus, adult. Fascicles of Heissner's-fibre axons enter the 

 mesocoele from tlie posterior side of the posterior commissure. X H7. 



Ahitera schoepfii, young, 15 cm. long. Reissner's fibre is formed almost 

 exclusively from fascicles of axons entering the ventricle anterior to the 

 posterior conmiissure. X ca. 100. 



IJiiombus triacanthus, young, 4 cm. long. Both the anterior and posterior 

 branches of Reissner's fibre are sliown. X 120. 



Saivelinus fontinalis. The section is somewliat oblique ; the anterior por- 

 tion of the figure is median ; the posterior portion parasagittal. Note 

 the anterior branches of Reissner's fibre entering the ventricle anterior 

 and ventral to the posterior commissure, and tlie posterior branches in 

 tlie recess above the commissure. X 120 

 Fig. 52. Gadus callarias, larvae, 15 mm. long. Reissner's fibre ventral to the pos- 

 terior commissure. X 385. 

 Fig. 53. Cynoscion regalis, adult. Transverse section of posterior commissure 



and Reissner's fibre. X 900. 

 Fig. 54. Another section of the same, showing more clearly the medullary sheath, 

 and the punctate appearance in transverse section of the axillary por- 

 tion, due to the cut ends of the constituent axons of Reissner's fibre. 

 X 1350. 



