II 



BEAIN 



03 



That this idea is unsound seems clearly to be indicated by such 

 series of sections as that shown in Fig. 53. As a matter of fact it 



Fig. 54. — Sagittal sections through the brain of Acanthias. (After Kupffer. ) 



A, 3*3 ram. embryo ; B, 7-8 mm. ; C, 10 mm. ; I), 27 mm. ; E, 70 mm. cer, cerebellum ; ch, optic 

 chiasma ; ect, external ectoderm ; h.c, habenular commissure ; inf, infundibulum ; M, cavity of mesen- 

 cephalon ; N, notochord ; n.p, anterior neuropore ; p.c, posterior commissure ; pin, pineal organ ; Rh, 

 cavity of rhombencephalon ; t.o, tectum optieum ; v } velitm transversum ; v.IV, fourth ventricle. 



seems probable that very pronounced flexure of the brain, such as is 

 seen in the developing Elasmobranch, is to be regarded as a secondary 



