Diamond M K
Department of Anthropology, University of Chicago, Illinois 60637.
J Morphol. 1989 Apr;200(1):71-86. doi: 10.1002/jmor.1052000109.
In primitive eutherians, the stapedial artery is the primary supplier of blood to the nonneural tissues of the head. Beyond a certain body size, the stapedial artery can no longer function as the sole supplier to its original territory because the diameter of its stem is limited by the size of the intercrural foramen of the stapes, which exhibits strong negative allometry. Some eutherians have extended the upper limit that the diameter of the stapedial stem can attain by developing a coarctation (narrowing) at the transcrual portion of the vessel. In the Norway rat (Rattus norvegicus) and the golden hamster (Mesocricetus auratus) the coarctation develops in postnatal life and is evidently caused by a retardation in growth that keeps the diameter of the vessel at infantile dimensions. In the rat, additional reduction in the external diameter is produced by a thinning of the tunica media of the arterial wall. A comfortable gap between the wall of the artery and the sides of the intercrural foramen is maintained that most likely facilitates the attenuation of potentially disruptive low-frequency vibrations produced by the arterial pressure pulse. The only negative side effect of a coarctation in rat-sized animals is that resistance to flow is increased and volume flow rate is concomitantly diminished. The coarctation does not create flow disturbances downstream of the constriction. One possible additional benefit of the coarctation is a flattening out of the arterial pressure pulse. It is speculated that the capacity to develop a coarctation once a certain body size is reached is an ancient trait that dates at least as far back as the Early Cretaceous.
在原始真兽类动物中，镫骨动脉是头部非神经组织的主要血液供应者。超过一定体型后，镫骨动脉无法再作为其原始供血区域的唯一供血者，因为其主干直径受镫骨脚间孔大小限制，而镫骨脚间孔呈现出强烈的负异速生长。一些真兽类动物通过在血管的跨脚部分形成缩窄（变窄）来扩大镫骨主干直径所能达到的上限。在挪威大鼠（褐家鼠）和金黄仓鼠（中仓鼠）中，缩窄在出生后形成，显然是由生长迟缓导致血管直径维持在幼年尺寸。在大鼠中，动脉壁中膜变薄导致外径进一步减小。动脉壁与镫骨脚间孔两侧之间保持着适度间隙，这很可能有助于减弱动脉压力脉冲产生的潜在破坏性低频振动。在大鼠体型的动物中，缩窄的唯一负面作用是血流阻力增加，体积流量随之减少。缩窄不会在狭窄下游产生血流紊乱。缩窄的一个可能的额外益处是使动脉压力脉冲变得平缓。据推测，一旦达到一定体型就能够形成缩窄的能力是一种古老的特征，至少可以追溯到早白垩世。
