THE MAMMALIAN BRAIN 
75 
by the hand. When it is finally free, place it in a deep dish of 
water, and examine it in its fresh condition. 
Finally harden it, for at least a week, in a mixture of alcohol 
and formalin (5% formalin in 30% alcohol), taking care to rest it 
upon cotton and not allow it to come in contact with the walls of 
the container. It is advisable that only one or two specimens 
should be hardened in a single container, and there should be at 
least a liter of the fluid for each specimen ( i.e ., 300 c.c. of 95% 
alcohol, 650 c.c. of water, and 50 c.c. of formaldehyde). Some of 
the hardening fluid should be gently forced by means of a syringe 
into the cavities of the brain through the opening in the stalk of 
the hypophysis upon the ventral surface. 
For the subsequent study of the brain it should be examined 
and dissected under water, and, after it is thoroughly hardened, it 
may be kept in water for several days without deleterious results. 
Preserve the head from which the brain was removed in 5% 
formalin. 
A. EXTERNAL FEATURES. 
Block out a general outline of the whole brain (xf) in very light 
lines from dorsal , lateral , and ventral aspects , and add to each 
drawing the various features as they are identified. 
1. Cerebrum (Telencephalon, Diencephalon, and Mesencephalon) 
Dorsal Aspect.- —Note that the roof of the telencephalon has 
become greatly thickened to form the two largest and most con¬ 
spicuous portions of the brain, the cerebral hemispheres, while the 
real anterior ends of the telencephalon, the slender olfactory 
lobes, are practically concealed from view. Note the deep 
median longitudinal fissure, separating the two hemispheres from 
each other; the frontal and occipital poles of the cerebral hemi¬ 
spheres, and the general division of each hemisphere into regions 
corresponding to the bones which form the cranial walls, and 
hence known respectively as the frontal, parietal, occipital, and 
temporal lobes. Note further that the convoluted appearance of 
the surface of the cerebral hemispheres is due to depressions, 
sulci, of varying depth, bounded by elevations or gyri. Note to 
what extent these are bilaterally symmetrical in arrangement. 
The sulci, the deeper of which are called fissures, may be followed 
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