Hence, we proposed a basic study to find out the existence of tonsillar ectopia ( Position of tonsils below the foramen magnum) in normal population. There are no Indian studies to corroborate the findings. Position of tonsils is of great importance in assessing the hind brain deformity–Chiari malformation. Western studies have shown the cerebellar tonsils to be below the foramen magnum. Normal position of the cerebellar tonsils is described to be at or above the foramen magnum. POSITION OF CEREBELLAR TONSILS IN REFERENCE TO FORAMEN MAGNUM: AN MRI STUDY The results of this analysis support the utility of foramen magnum position as an indicator of bipedal locomotion in fossil hominins. Among the primates sampled, humans exhibit the most anteriorly positioned foramina magna. The foramen magnum is also situated more anteriorly in orthograde strepsirrhines than in pronograde or antipronograde strepsirrhines. Our comparative data reveal that bipedal marsupials and rodents have foramina magna that are more anteriorly located than those of quadrupedal close relatives. Additionally, we examine whether strepsirrhine primates that habitually assume orthograde trunk postures exhibit more anteriorly positioned foramina magna compared with non-orthograde strepsirrhines. Here, we test the hypothesis that an anteriorly positioned foramen magnum is related to bipedalism through a comparison of basicranial anatomy between bipeds and quadrupeds from three mammalian clades: marsupials, rodents and primates. Nonetheless, previous studies have struggled to validate the functional link between foramen magnum position and bipedal locomotion. Accordingly, the relative placement of the foramen magnum on the basicranium has been used to infer bipedal locomotion and hominin status for a number of Mio-Pliocene fossil taxa. The anterior position of the human foramen magnum is often explained as an adaptation for maintaining balance of the head atop the cervical vertebral column during bipedalism and the assumption of orthograde trunk postures. Foramen magnum position in bipedal mammals.
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