[Two pairs of particular structures of mandibular joints of mammalian sorex].
The mandibular joints of Chinese Anouroserex squamipes, spuamipes, MILNE-EDWARDS were examined by gross and microscopic studies. We discovered that there were two pairs of joints in these animals. The upper pair of joints, named lateral mandibular joints, were placed on both sides under the parietal bone. The lower pair of joints, named skull-base mandibular joints, were placed on both sides of the skull-base. These two pairs of joints could not be observed simultaneously in the same plane either sagittally or frontally. The lateral fossa and condyle were obliquely from outward, backward and upward to inward, forward and downward on both sides; the fossa looked like a groove concave downward, and the head of the condyles appeared in a cylindrical form. The lower fossae and condyles were transversely forward and inward from the lateral mandibular joints; the fossa looked like a shallow spoon concave upward, and the condyle appeared in a flat surface to fit the upward fossa. The sorex likes to dig holes on the ground to live in and search for insects in the soil to eat. The skull-base mandibular joints will support the jaw to counteract the digging force and protect the lateral mandibular joints from injury. This study has suggested that the morphology of the mandibular joints is adapted to their functional requirements during evolution.
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D000818:Animals; D007312:Eulipotyphla / Q000033:anatomy & histology*; D008334:Mandible / Q000033:anatomy & histology; D013704:Temporomandibular Joint / Q000033:anatomy & histology*