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Facial and Masticatory Muscles |
Photos and text by Alexandra Sardi and Janelle Cooper Dissection Notes: We began the dissection of the lower limb at the femoral triangle, exposing the femoral artery, nerve and vein. The medial muscles were more easily exposed due to the fact that the fascia was much thinner and easier to peel on that side. On the lateral side, we encountered thick, tough fascia that graded into an iliotibial tract and was difficult to remove. In fact, part of the biceps femoris muscle was removed along with the fascia. Furthermore, we found that the gluteal and hamstring area of the rabbit has incredibly thick muscles, much more so than does the lower leg that is rather thin. Skinning the pes was also difficult as the skin was tightly bound to the fascia. Discussion: Upon removing the fascia from the lateral part of the thigh, the first identifiable muscles are the gluteus superficialis, biceps femoris and vastus lateralis (1). Upon cutting and reflecting the first two, the gluteus medius becomes visible. The semimembranosus and semitendinosus are also more easily seen on the posterior side. In the deep layer, one can identify the gemelli (major/minor), obturator internus and externus, quadratus femoris and piriformis (2). In the rabbit, the gemellus major and gemellus minor are actually one continuous muscle, so the division into “major” and “minor” is arbitrary. The sciatic nerve is also visible near the piriformis muscle, as it passes through the sciatic notch. This large nerve innervates the muscles found in the posterior region of the thigh and originates from the seventh lumbar and first sacral nerves (3). On the medial side of the femur, one of the most notable parts is the femoral sheath, which contains lymph node, the femoral artery and the femoral vein. The femoral nerve runs on the lateral side of the femoral sheath. There are several visible superficial muscles such as gracilis, rectus femoris, vastus medialis, sartorius, tensor fasciae latae and biceps femoris (2). As could be expected of most cursorial animals, the rabbit’s muscle bellies are bunched close to the trunk and the lower leg has mostly tendons. This makes the lower legs lighter and allows the rabbit to run faster (1). It’s interesting to note the relative size of the gracilis in the rabbit and other quadrupedal mammals as compared to that of humans. In the rabbit, for example, gracilis is a thick and wide medial muscle whereas in humans it’s thin, long and “gracile” (hence the term gracilis). Compared to other cursorial mammals, the rabbit had much larger thigh and leg extensors than most other cursorial animals in lab. The rabbit is a cursorial mammal but has a very unique style of locomotion: half-bounding (1). In half-bounding, the two hind feet touch the ground almost in unison but the forefeet alternate (3). The time the forefeet spend on the ground is shorter at all speeds. This creates a gait in which the hind legs are much more important in providing the force than the forelimbs (3). The rabbit depends on the amount of force it can exert with its hind limbs to escape from predators so the huge extensor muscles make sense. The pectineus is also particularly curious because anatomists can’t seem to agree on whether it has a dorsal or ventral origin. In mammals, the pectineus is one of the three muscles that differentiate from the puboischiofemoralis internus of lower tetrapods. The puboischiofemoralis is a dorsal muscle, so we believe that the pectineus should also be classified as a dorsal muscle (1).
(1, 2, 3) 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.
