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Facial and Masticatory Muscles |
Photos and Text by: Janelle Cooper and Alexandra Sardi Dissection Notes: Before beginning our dissection, we inspected the exterior of the rabbit to identify the sex and make sure it was not missing any exterior organs or limbs. We determined that the rabbit was a male and intact. We also determined that the rabbit is a plantigrade animal. We began our dissection with a transverse incision cranial to the pelvis on the ventral side of the rabbit. We then cut along the coronal plane halfway between the shoulder and the hip. We skinned the rabbit, beginning at the abdomen and working towards the neck. The skin was easily removed, but it was hard to leave the panniculus carnosus muscle, or cutaneous trunci muscle, intact and a lot of it was removed with the skin. The skin was especially difficult to remove at the origination points for this muscle, the lateral inferior side of the scapula. It is important to note that we left the skin attached in places that we were not going to dissect in order to keep them from drying out. Once the skin was removed, we began our dissection by identifying the superficial muscles. They were very easy to identify. In order to reach the deep muscles, we cut the rhomboidius thoracis muscle at its insertion on the vertebral border of the scapula. We cut both the supraspinatus and the infraspinatus muscles at their insertions on the greater tuberosity of the humerus bone, attempting to conserve their attachments at their origins. We then reflected the scapula to see the muscles that lay deep to the bone. Due to the very unusual way that we dissected the shoulder, it is possible to see that the serratus ventralis thoracis and serratus ventralis cervicis muscles are visibly connected as one muscle layer deep to the rhomboideus muscles. Discussion: The cutaneous muscle, cutaneous trunci, was the first muscle we could easily distinguish on the rabbit. This muscle is used to twitch the skin and has the same developmental origin as muscles such as the platysma, spanning the throat, and other more specialized muscles such as the levator labii superioris and depressor labii mandibularis which are extremely important in allowing herbivorous animals, such as the rabbit, to grasp the vegetation with their lips. The cutaneous trunci is not very large in the rabbit and does not have any real function other than shaking off insects (1). The shoulder muscles of the rabbit were larger and more developed than we had expected. While the rabbit uses mostly its hind limbs during locomotion, its forelimbs are important for digging and it makes sense that the shoulder muscles would be large. The rabbit does not possess a clavicle (2,3). For this reason, it has a sternomastoideous muscle instead of a sternocleidomastoideus muscle and does not possess a cleido-occipital muscle (2). In the rabbit, the sternomastoideus muscle originates on the manubrium of the sternum and on the mastoid process. The trapezius muscle in the rabbit has two parts: pars cervicalis and pars thoracica. Furthermore, the rabbit has three pectoralis muscles: pectoralis superficialis descendens, pectoralis superficialis transversus and pectoralis profundus. The first two can be differentiated easily by the striations and the third can be separated simply because it lies deep to the other two (3).
Adapted from [2] References: 1. Kardong, Kenneth V., Vertebrates: Comparative Anatomy, Function, Evolution. McGraw Hill, New York: 2002. 2. McLaughlin C.A., Chiasson R.B., Laboratory Anatomy of the Rabbit, McGraw-Hill, New York: 1990. 3. 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.
