The brain is well developed in marine mammals and bony processes extending between several lobes can make removal difficult. In the brain, the outer layer of tissue is composed of cell bodies which constitute gray matter while in the spinal cord, the outer layer of tissue is composed of the axons that carry information away from the cell body. Most axons are covered in a layer of fat which insulates the electrical signals much like shielding on electrical wires. Thus, the outer appears of the spinal cord is white. Like in humans, the raised structures on the surface are called gyri (gyrus singular) while the valleys between are called sulci (sulcus singular).
At necropsy, the brain should be removed using a bone saw and then carefully place into a formalin solution whole, unless fresh or frozen tissue samples are needed. The brain is very fragile and it would be very difficult to look at unfixed cross sections. A good technique for handling the brain is to place it onto 3-4 paper towels and use this as a sling to carefully lower the organ into a formalin solution. Because the brain is very large, several changes of the formalin solution will be needed to completely fix the whole tissue.
Detailed annotated images of the nervous system in a harbor porpoise are shown below.
