s largely upon the question whether there is really a 
i homology between the superior and posterior commissures 
some valuable data as to the primitive condition of the enceph- $ 
f there is no such homology between these commis- 
» ‘nere yet remains considerable ground for the supposition 
t the inter-vesicular folds are simply lines of retarded growth 
the walls and roof of the tube to be traversed at an early * 
riod by the commissures.—Henry F. Osborn. 
EXPLANATION OF CUTS. 
a Diagrammatic longitudinal section of the frog’s brain at an early stage, 
ming the division of the neural tube into the prosencephalon, p ; thalamenceph- 
i mesencephalon, m; and metencephalon, m/. The letters are placed in the 
“Ive ventricles, ‘ 
2. Camera drawing of a vertical section of the frog’s brain ata later stage, © 
the dorsal commissures occupying the inter-vesicular folds. Sem, superior 
reo, 2, Posterior commissure ; cé/, cerebellum; %24, infundibulum; acm, 
= Ommissure; x, pineal gland. 
3 
Bae drawing of a horizontal section of the frog’s brain at the same 
"8 Me commissures traversing the folds. 
and Stream for Jul i he results of his Poe 
y 14, 1887, gives the resul” ivy it 
He ‘shows that the accéuht given by MacGilwny = 
$ 
