Kuratani Shigeru
Laboratory for Evolutionary Morphology, RIKEN Center for Biosystems Dynamics Research (BDR) and RIKEN Cluster for Pioneering Research (CPR), Kobe, Hyogo 650-0047, Japan.
Genesis. 2018 Jun;56(6-7):e23213. doi: 10.1002/dvg.23213.
Cranium of jawed vertebrates is composed of dorsal moiety that encapsulates the brain, or the neurocranium, and the is called the neurocranium, and the ventral moiety, the viscerocranium, that supports the pharynx. In modern jawed vertebrates (crown gnathostomes), the viscerocranium is predominantly of neural crest origin, and for the neurocranium, the rostral part is derived from neural crest cells, whereas the posterior part from the mesoderm. In the cyclostome cranium, the mesoderm/neural crest boundary of the neurocranium used to be enigmatic, let alone the morphological comparison of neurocranial between two cyclostome groups, lampreys and hagfishes. By examining the hagfish development it has become clear that cyclostomes share a common craniofacial embryonic pattern that is not shared by modern gnathostomes, and cyclostome cranium can be compared among the group as developmental modular units with comparable mesoderm/neural crest boundary within the neuroranium. Also, the dual origin of the jawed vertebrate neurocranium has now turned out to represent a derived condition, and ancestrally, the neurocranium would likely have been predominantly of mesodermal origin. Enlargement of the forebrain and reorganization of the oral apparatus seem to have led to the involvement of the neural crest in the rostral neurocranium.
有颌脊椎动物的颅骨由包裹大脑的背侧部分（即脑颅）和支撑咽部的腹侧部分（即咽颅）组成。在现代有颌脊椎动物（冠群有颌类）中，咽颅主要起源于神经嵴，而脑颅的前部源自神经嵴细胞，后部则源自中胚层。在圆口类动物的颅骨中，脑颅的中胚层/神经嵴边界一直是个谜，更不用说对七鳃鳗和盲鳗这两个圆口类动物群体的脑颅进行形态学比较了。通过研究盲鳗的发育过程，已经清楚地表明，圆口类动物具有一种现代有颌类动物所没有的共同颅面胚胎模式，并且圆口类动物的颅骨可以作为发育模块化单元在群体中进行比较，其神经颅内部具有可比的中胚层/神经嵴边界。此外，有颌脊椎动物脑颅的双重起源现在已被证明是一种衍生状态，在祖先状态下，脑颅可能主要起源于中胚层。前脑的扩大和口器的重组似乎导致了神经嵴参与到脑颅的前部。
