RHINENCEPHALON OF DELPHINUS 509 
elsewhere. The other part of the cortical covering, divided from 
the frontal cortex by one or two shallow furrows, is made up of 
gray matter covered by a medullated nerve layer of very fine 
fibers. This layer of nerve fibers is pushed down here and there 
into little processes, which project into the underlying gray 
substance and thus give a somewhat undulated appearance to 
the outline of the latter. 
18! ee ee iy 
16) ee eae 169 
143 eel = aE 43 
125 SARAH 125 
Fig. 6 Median sagittal section of brain of adult dolphin. The numbered 
lines indicate the planes and positions of the sections which have been drawn. 
In comparison with brains of macrosmatic animals, it shows a rounded form in 
the frontal region, and not a tapering form. The floor of the central canal of the 
brain recurves, as it descends from the aqueduct of Sylvius to the posterior wall 
of the infundibulum. The corpus callosum is large and well-arched. The anterior 
commissure is very small. X #. 
It is more than probable that this slightly convoluted cortical- 
like plate, which lies just where we are accustomed to see the 
more distinctly convoluted cortex of the lobus parolfactorius, 
constitutes the last remnants of this formation. 
Laterally (fig. 11) the medullated fibers are more numerous 
and more closely packed, so that the lateral aspect of the nucleus 
lentiformis is covered only by a relatively thin layer of grayish- 
