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The skull can be divided into two parts: the neurocranium, which forms a protective case around the brain, and the facial skeleton, which forms the skeleton of the face. In mammals, the neurocranium, braincase, brainpan, or brain-pan〔(【引用サイトリンク】work=Merriam-Webster/Medical )〕 is the back part of the skull and houses the brain. The interorbital region lies in front of the neurocranium. In the human skull, the neurocranium includes the calvaria, or skullcap. The lower part of the skull is the facial skeleton also known as the splanchnocranium. Evolutionarily, the human neurocranium has expanded from comprising the back part of the mammalian skull to being also the upper part: during the evolutionary expansion of the brain, the neurocranium has overgrown the splanchnocranium. The upper-frontmost part of the cranium also houses the evolutionarily newest part of the human brain, the frontal lobes. The term "cranium" can be ambiguous in that it can refer to the neurocranium alone or to the whole skull (the neurocranium and the facial skeleton). ==Structure== The size of the braincase is variable among mammals. The roof may contain ridges such as the temporal crests. Below the braincase is a complex of foramina (openings) and bones, including the foramen magnum which houses the neural spine. The auditory bullae, located in the same region, aid in hearing.〔Elbroch, M. 2006. Animal skulls: A guide to North American species. Stackpole Books, pp. 20–22. ISBN 978-0-8117-3309-0〕 The neurocranium is formed by the endocranium, the lower portions of the cranial vault, and the skull roof. These are not fused in fishes, and a proper neurocranium is only found in land vertebrates. The neurocranium is divided into two portions: (a) the membranous part, consisting of flat bones, which surround the brain as a vault; and (b) the cartilaginous part, or chondrocranium, which forms bones of the base of the skull.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「neurocranium」の詳細全文を読む スポンサード リンク
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