Ashwell Ken W S, Gurovich Yamila
Department of Anatomy, School of Medical Sciences, The University of New South Wales, 2052, New South Wales, Australia.
Department of Anatomy, School of Medical Sciences, The University of New South Wales, 2052, New South Wales, Australia; CIEMEP, CONICET-UNPSJB, Roca 780, Esquel, 9200, Chubut, Argentina.
Zoology (Jena). 2019 Jun;134:38-57. doi: 10.1016/j.zool.2019.04.002. Epub 2019 Apr 9.
We have made quantitative volumetric analyses of cerebral cortical (pallial) structures in the brains of three species of monotreme (Ornithorhynchus anatinus, Tachyglossus aculeatus, Zaglossus bruijni) and compared the findings with similar measurements in a range of therian mammals (6 marsupials and 50 placentals). We have found that although the iso- and periallocortical grey matter volume of the monotremes is about what would be expected for their brain size, the proportion of iso- and periallocortical white matter in monotremes is substantially lower than that in the forebrains of therians. This suggests that the forebrains of the three monotremes have fewer association, commissural and/or projection connections than those of similarly sized forebrains of therian mammals. We also found that the iso- and periallocortex of the platypus is relatively smooth-surfaced compared to similarly sized brains of therian mammals, with a distinct caudal shift in the positioning of cortical white matter in the forebrain, consistent with expansion of the posterior thalamic radiation. Central laminated olfactory structures (anterior olfactory nucleus and piriform cortex) are large in the tachyglossid monotremes (Tachyglossus aculeatus and Zaglossus bruijni) and large in xenarthran placental mammals, suggesting convergence of the forebrain structure of monotreme formivores with that of similarly specialized therians like the xenarthrans Myrmecophaga tridactyla and Dasypus novemcinctus.
我们对三种单孔目动物（鸭嘴兽、针鼹、原针鼹）大脑中的大脑皮质（脑皮层）结构进行了定量体积分析，并将结果与一系列有胎盘类哺乳动物（6种有袋类动物和50种胎盘类动物）的类似测量结果进行了比较。我们发现，尽管单孔目动物的等皮质和近等皮质灰质体积与其脑大小预期的大致相同，但单孔目动物中等皮质和近等皮质白质的比例明显低于有胎盘类哺乳动物前脑的比例。这表明，这三种单孔目动物的前脑与同样大小的有胎盘类哺乳动物前脑相比，其联合、连合和/或投射连接较少。我们还发现，与同样大小的有胎盘类哺乳动物大脑相比，鸭嘴兽的等皮质和近等皮质表面相对光滑，前脑皮质白质的位置有明显的尾侧移位，这与丘脑后辐射的扩展一致。在针鼹科单孔目动物（针鼹和原针鼹）以及异关节胎盘类哺乳动物中，中央分层嗅觉结构（前嗅核和梨状皮质）较大，这表明食蚁单孔目动物的前脑结构与同样特化的有胎盘类动物如食蚁兽和九带犰狳的前脑结构趋同。
