Comparative Medicine Branch

Virtual Mouse Necropsy

Step 12: The Brain

Dorsal View

1. Olfactory lobes
2. Cerebrum
3. Cerebellar hemisphere
4. Cerebellum
5. Pineal gland

Ventral View

1. Olfactory lobes
2. Cerebrum
3. Optic nerves
4. Median eminence
5. Pituitary gland
6. Cerebellum
7. Medulla

General Procedures

If you are interested in structures above the neck, cut off the head. Skin the fur from the head and discard. Cut the jaw off by sliding your scissors through the oral cavity until you meet the resistance of the mandibular junction, and cut on both sides. You can examine the oral cavity at this point for any abnormalities. If you suspect nasal obstructions, slide a needle into the nasopharyngeal opening located behind the soft palate and flush with saline or preservative. If there is no blockage, the fluid will empty through the nostrils. Check to see if the Harderian glands located behind and and around the edge of the eye socket are enlarged. You do not have to remove the eye for this observation, but if you can see a great deal of tissue poking out from the edge of the eye, it is very likely it is an enlarged Harderian gland.

Bone Structure of Mouse Skull

1. Nasal bone
2. Nasal process of incisive bone
3. Eye socket
4. Maxilla
5. Zygomatic bone
6. Zygomatic process of squamous part
7. Frontal bone
8. Interparietal bone
9. Occipital bone

Removal of the Brain

Next, remove any excess tissue or muscle from the cranium. A membrane surrounds the surface of the cranium and may cause problems if not removed, so use your scissors to remove it as you would trim the cuticles of your fingernails. If you removed the head properly, you should be able to see the cerebellum at the back of the cranium. If not, trim away the excess spinal tissue until you reach this point. Now it is time to remove the brain. Using your scissors, cut along the natural sagittal sutures in the skull, making sure you keep your scissors tips up to avoid injury to the brain. Reflect back the bones as you go until you are cutting between the eyes. Gently take your forceps and just slightly pinch the surface of the brain. Hopefully, you will lift up the meninges (the lining of the brain and spinal cord) and you will be able to remove it. If you forget this step, you could inflict serious damage to the brain on removal. Turn the head upside down and use your forceps to help you ease the brain out of the skull. At some point, you will see two thread-like structures anchoring the brain from its ventral side. These are the optic nerves; use your forceps to snip them loose. Now take your forceps, and gently ease the brain out of the skull.

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