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Facial and Masticatory Muscles |
Photos and text by Janelle Cooper and Alexandra Sardi Dissection notes: The dissection of the pes and lower leg was especially difficult because the skin is so tightly adhered to the muscle and fascia. Furthermore, removing the fascia itself was incredibly difficult. The muscles on the leg are highly compartmentalized and enveloped in an extremely thick fascia. Towards the foot we noticed retinacula surrounding the tendons. The feet were covered with fur, which is a light way of helping to pad the feet. Most of the muscles of the foot were easily identified. Discussion: After skinning the leg, the first superficial muscles that we could see were the gastrocnemius, peroneus longus and tibialis anterior. Upon reflecting the gastrocnemius, a lot of the deeper muscles became visible. These included the soleus, extensor digitorum longus, extensor digitorum lateralis and peroneus muscles. The lateral saphenous vein and popliteal lymph nodes were also visible in the popliteal area, as was the tibial nerve. Around the ankle, there were various retinacula: the crural retinaculum of extensors; tarsal retinaculum of extensors, and; retinaculum extensorum proximale. Dissection of the rabbit’s ankle showed what we expected, considering the rabbit’s half-bound gait. The rabbit can plantarflex and dorsiflex at the tibiotalar joint, which allows for a lot of movement (1). However, the subtalar joint does not allow much inversion and eversion of the foot. This makes sense because the rabbit needs to plantarflex and dorsiflex in order to hop and half-bound but having a lot of room for inversion and eversion would probably just mean more injuries while moving. The rabbit does not pronate or supinate the foot so there is not motion in the calcaneocuboid joint (1). Different animals have adapted to increase their speed in different ways. Digitigrades, and unguligrades, in the extreme, lengthen their limbs by standing on their digits or tiptoes respectively. Unguligrades and digitigrade have longer metatarsals and unguligrades lose digits or their phalanges may fuse together. Often the third metatarsal will be the longest and bear most the weight (1). This allows these animals to increase their limb length and their stride length. In class, we saw an unguligrade pig, which did not have fused phalanges but did bear its weight mostly on the third and fourth digits. The cat was digitigrade and had relatively long metatarsals as well. The rabbit, however, is plantigrade and had shorter metatarsals and shorter limbs. The rabbit gets away with its plantigrade posture because it uses the half-bound. While the rabbit did not increase its limb length, it increases its stride length by increasing the force with which it can push off the ground and the degree to which it flexes and extends the vertebral column. The rabbit can use extra force to push off the ground because during the half-bound, both of its muscular hind limbs reach the ground and push off at almost the exact same time (2). This gives the rabbit extra spring.
Adapted from: (1, 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 Coulour Atlas of Anatomy of Small Laboratory Animals, V1. Wolfe Publishing Ltd. London, England: 1992.
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Artwork: Weil, from Stubbs' 1776
"Anatomy of the Horse."
Background free from Eos Development, with
slight color modification.
