Fox brain
Photo and text: Nick Zolkowski and Elizabeth Farrell
Together, the spinal cord and brain comprise the central nervous system. Neural signals are propagated to the brain via afferent (sensory) neurons, and neural signals leave the brain via efferent (motor) neurons. In mammals, the largest portion of the brain is the cerebrum, which is separated from the cerebellum by the cerebral transverse fissure. The cerebrum is divided into a left and right hemisphere by the corpus callosum, which functions to link corresponding signals between the two hemispheres. The cerebrum is divided into the frontal, parietal, temporal, and occipital lobes. [1] The frontal lobe houses the primary motor area of the cerebral cortex. Caudal to the frontal lobe and lateral to the parietal lobe is the temporal lobe, where the auditory area is found. Also in this lobe is the somesthetic area, responsible for tactile and kinesthetic input. Caudal to the parietal lobe is the occipital lobe, where the visual area is located. At the caudal aspect of the brain is the cerebellum, which serves to coordinate movement. [1]
We began the lab by removing the left and right temporalis muscles from the top of the skull by detaching them from their attachments on the sagittal, frontal and nuchal crests and from the zygomatic arch. The attachments on the zygomatic arch were particularly difficult to remove. After the muscles had been cleared, we were able to see the top of the skull. Using a chisel, we cracked the parietal and temporal bones with relative ease. As we removed the components of the skull, we could see grooves in the underside of the chips. These impressions correspond with the veinous sinuses.
As we continued removing fragments of the skull, we could see the brain. Most of what we saw was the gyre and sulci (folds and grooves) of the cerebrum. Posterior and inferior to the cerebrum is the cerebellum. As shown in the picture, the cerebrum comprises the majority of the brain. However, it is not as large, proportionally, as the cerebrum of higher order mammals' brains, such as great apes and humans. Separating the cerebellum and cerebrum is the tentorium osseum, a bony plate that was difficult to remove during dissection. The presence of the tentorium osseum is primitive for Carnivora, and is also found in pangolins and aardvarks [2]. Upon removal of the tentorium osseum, we found that our brain had not been well preserved, and would most likely not be able to be removed intact.
We removed the brain by cutting below the base of the cerebellum, through the brain stem and spinal cord. Due to poor preservation, some structures did not remain attached. Further, as it lies outside the dura mater, the pituitary gland remained fastened in the sella turcica. On the ventral side of the brain, the cerebral arterial circle, which provides blood supply to the cerebrum, was well-defined. The circle is comprised of the posterior cerebral, posterior communicating, internal carotid, anterior cerebral, and anterior communicating arteries. The anterior and middle cerebral arteries are branches off the internal carotid arteries, and the posterior cerebral arteries branch from the basilar artery, which results from the union of the two vertebral arteries. The cerebellum is supplied mainly by branches of the vertebral and basilar arteries.[3]
1.Miller, Malcolm E. 1952. Guide to the Dissection of the Dog. (3rd Ed). Edward Brothers Inc., New York.
2. Shoshani and McKenna, 1998. Higher taxonomic relationships among extant mammals based on morphology, with selected comparisons of results from molecular data. Molecular Phylogenetics and Evolution. 9(3):572-584
3.Agur, A. and Lee, M. 1999. Grant's Atlas of Anatomy. (10th Ed.). Lippincott Williams and Wilkins, Baltimore, MD.
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