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Facial and Masticatory Muscles |
Text and Photos by Janelle Cooper and Alexandra Sardi Dissection Notes: We began the dissection by cutting medially from the pinnae (auricles) to the nose and peeling back the skin. It was difficult to remove the skin without removing facial muscle along with it. In fact, a few muscles were lost in the skinning process. These muscles included parts of the levatori nasolabialis, zygomaticus and some of the folliculi pilorum. We also removed the skin behind the ears to reveal the parotid gland. Due to its resemblance to fatty tissue, we almost removed the parotid gland while skinning the rabbit. Discussion: Rabbits are strictly herbivorous. Although they generally prefer grasses, they will eat forbs when available. They may also eat woody plants, stems, leaves and fruits of shrubs when there are no grasses available (1). Herbivorous animals often use their lips to grasp and retrieve their food, so we expected the lip muscles to be large to aid in feeding. This was true for orbicularis oris, which closes the lips, as well as for levator nasolabialis, which moves the upper lip. Both aid in grasping grass, as does the zygomaticus portio auricularis, which controls the corner of the mouth (2). Another interesting action that rabbits perform is the twitching of the nose and vibrissae. The levator labii superioris muscle aids these motions, but it was too deep and small to be identified (2). The masseter and temporalis muscles elevate the jaw in mammals. We were easily able to identify these muscles in the rabbit. Rabbits have comparatively large masseter muscles, similar to most other herbivorous animals (3). The cat, a carnivore that was dissected in class, had a much larger temporalis muscle and the masseter was comparatively small. This ratio of the temporalis to the masseter holds true when comparing most carnivorous and herbivorous animals. Rabbits have long ears that move independently to give them both keen hearing and an efficient method of releasing heat. For this reason, they need strong extrinsic ear muscles such as scuturuauricularis superficialis, zygomaticus portio auricularis and frontoscutularis portio temporalis. Rabbits do not use facial expressions to communicate; therefore we did not expect to find specialized muscles of communication. The only muscle that we found that could be used for communication was the platysma, which is responsible for moving the skin of the lower face. This muscle is small when compared to the platysma of other mammals that use facial expression. Two major nerves innervate the muscles of the face. The first branchial arch (mandibular) is innervated by the fifth cranial nerve while the second branchial arch (hyoid) is innervated by the seventh cranial nerve (4).
Adapted from [3]
Adapted from [2] References: 1. Thompson, Harry V. and King, Carolyn M., The European Rabbit, Oxford University press, Oxford: 1994. 2. Kardong, Kenneth V., Vertebrates: Comparative Anatomy, Function, Evolution. McGraw Hill, New York: 2002. 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. |
Artwork: Weil, from Stubbs' 1776
"Anatomy of the Horse."
Background free from Eos Development, with
slight color modification.
