Shoulder

Brachium

Antebrachium

Facial and Masticatory Muscles

Thorax and Heart

Brain

Body Wall

Hip and Thigh

Shank and Foot

Digestive System

Urinary and Reproductive Systems

Hip and Tail

Brain of the Rabbit (Oryctolagus cuniculus)

Photos and text by Janelle Cooper and Alexandra Sardi

Introduction:

The brain of the rabbit is made up of four parts: the forebrain, the midbrain, the hindbrain, and the brain stem (1).  The forebrain is composed of the two cerebral hemispheres, the corpus callosum, the infudibulum, and cranial nerves I (olfactory nerve) and II (optic nerve).  The midbrain, or mesoencephalon, contains cranial nerve III (oculomotor nerve).  The hindbrain is composed of the pons, cerebellum, and cranial nerve V (trigeminal nerve).  Finally, the brain stem is mainly made up of the medulla oblongata (1).

Dissection Notes:

We began this dissection by scraping away the temporalis muscle from the anterior portion of the skull.  Once the skull was visible, we used scissors to cut around the perimeter of the skull, making sure not to damage the brain.   We found it very difficult to cut through the skull because the bone was harder and thicker than most of the other bones in the rabbit’s body.  We removed the top of the skull and noticed that the dura mater came off attached to the inside of the skull.  Using a probe, we gently lifted the brain out of the head.  We then cut the brain stem, fully freeing the brain from the rabbit’s head.  Inside of the brain case, we saw the optic chiasm where the optic nerves cross and then enter the brain.  Still attached to the brain was one of the two optic nerves.

The brain stem extends into the spinal cord along the dorsal side of neck.  With the rabbit laying on its ventral side, so that the dorsal side was facing us, we cut away neck musculature to reveal the spinal cord and surrounding vertebrae.  This was difficult because the neck muscles were fairly thick.

To divide the brain into its right and left hemispheres, we used a scalpel cut down the longitudinal fissure of the brain.  The interior view of the brain revealed the third and fourth ventricles as well as the corpus callosum.  In addition, a distinct separation between the pons and medulla oblongata were visible.        

Discussion:

The brain of the rabbit was smooth with little to no sulci at all.  The opossom, beaver, and rat also have smooth brain surfaces lacking sulci.  The pig, although fetal, did in fact have surface fissure on the brain, giving it a wrinkled appearance.  The longitudinal fissure divided the brain into left and right cerebral hemispheres.  At the anterior end of the brain were the two olfactory bulbs.  These are extensions of the brain where the processing of smell occurs (1,2).   In the rabbit, the olfactory bulbs were huge.  This is because the rabbits rely heavily on their sense of smell as do the cat and rat which also had large olfactory bulbs (2).

When we removed the brain, the pituitary gland was destroyed.  However, we were still able to still the infundibulum, which attaches the pituitary to the brain (3).  The cerebral arterial circle surrounded the infundibulum.  The cerebral arterial circle is formed by connecting arteries from the basilar artery, the largest artery of the brain, which runs down the midsection of the brain (3,4).  There is considerable variation among different cerebral arterial circles of the animals present in class.  In fact, there is considerable variation, even within a species (1).  

In the hindbrain, the pons and trigeminal nerve were hard to discern but they were visible.  The cerebellum, however, was incredibly well preserved and its lobes were clearly identified.  In the rabbit, the paraflocculus is also very large and easily identified.  The medulla oblongata was removed, along with the brain and was seen in our dissection.  The smaller nerves of the brain were not clearly seen due to the small size of the specimen.  The only cranial nerves we could identify were the olfactory nerve, optic nerve and  trigeminal nerve.  The hypoglossal nerve was cut during the dissection and the others were cut or they are too small to identify.  

Adapted from (4)

References:

1. Kardong, Kenneth V., Vertebrates: Comparative Anatomy, Function, Evolution. McGraw Hill, New York: 2002.

2. Kent,G.C., Comparative Anatomy of the Vertebrates, McGraw-Hill, New York: 2001.

3. McLaughlin C.A., Chiasson R.B., Laboratory Anatomy of the Rabbit, McGraw-Hill, New York: 1990.

4. Popesko, P., Rajtova V., Horak J., A Colour Atlas of Anatomy of Small Laboratory Animals, V1.  Wolfe Publishing Ltd. London, England: 1992.