Costeur Loïc, Mennecart Bastien, Müller Bert, Schulz Georg
Naturhistorisches Museum Basel, Basel, Switzerland.
Biomaterials Science Center, University of Basel, c/o University Hospital Basel, Basel, Switzerland.
J Anat. 2017 Feb;230(2):347-353. doi: 10.1111/joa.12549. Epub 2016 Oct 11.
Foetuses are a source of scientific information to understand the development and evolution of anatomical structures. The bony labyrinth, surrounding the organ of balance and hearing, is a phylogenetically and ecologically informative structure for which still little concerning growth and shape variability is known in many groups of vertebrates. Except in humans, it is poorly known in many other placentals and its prenatal growth has almost never been studied. Ruminants are a diversified group of placentals and represent an interesting case study to understand the prenatal growth of the ear region. We computed tomography -scanned five cow foetuses and an adult petrosal bone (Bos taurus, Artiodactyla, Mammalia), and describe the bony labyrinth when already ossified. The foetuses encompass the second half of the 9.3-month-long gestation period of the cow. They were sampled at different ontogenetic stages to understand how and when the petrosal bone and bony labyrinth ossify in ruminants. The petrosal bone and bony labyrinth ossify within about 20 days in the fourth month of gestation. The bony labyrinth is already fully ossified at least in the 6th month, while only the cochlea, most of the vestibule and the common crus are already ossified at the beginning of the 4th month. The pars canalicularis of the petrosal thus ossifies at last. The size and volume of the bony labyrinth stay similar from the 6th month (possibly even from the 5th). From the end of the 4th month of gestation, a progressive lengthening of the cochlear aqueduct and endolymphatic sac occurs, culminating in the adult form and partly explaining the larger volume of the later. The inner ear in the cow ossifies quickly during the gestation period, being fully ossified around mid-gestation time, as in humans. The adult size and most of its volume are reached by mid-gestation time while the petrosal bone and skull still grow. A negative ontogenetic allometry between the bony labyrinth and the petrosal bone and skull is thus observed. It matches the evolutionary negative allometry of the structure observed in earlier studies. Few changes occur after ossification is achieved; only open structures (i.e. cochlear aqueduct and endolymphatic sac) continue to grow after birth and reflect size increase of the petrosal bone.
胎儿是了解解剖结构发育和进化的科学信息来源。包围平衡和听觉器官的骨迷路，在系统发育和生态学上是一个具有信息价值的结构，然而在许多脊椎动物类群中，关于其生长和形状变异性的了解仍然很少。除了人类，在许多其他胎盘类动物中对其了解也很少，并且几乎从未研究过其产前生长情况。反刍动物是胎盘类动物中的一个多样化群体，是了解耳部区域产前生长的一个有趣案例研究。我们对五头奶牛胎儿和一块成年颞骨（Bos taurus，偶蹄目，哺乳纲）进行了计算机断层扫描，并描述了已经骨化的骨迷路。这些胎儿涵盖了奶牛9.3个月妊娠期的后半段。在不同的个体发育阶段对它们进行采样，以了解反刍动物颞骨和骨迷路如何以及何时骨化。颞骨和骨迷路在妊娠第四个月内约20天内骨化。骨迷路至少在第6个月时已完全骨化，而在第4个月初只有耳蜗、大部分前庭和总脚已经骨化。因此，颞骨的小管部最后骨化。从第6个月（甚至可能从第5个月）开始，骨迷路的大小和体积保持相似。从妊娠第4个月末开始，耳蜗导水管和内淋巴囊逐渐延长，最终形成成年形态，这部分解释了后期较大的体积。奶牛的内耳在妊娠期迅速骨化，在妊娠中期左右完全骨化，与人类情况相同。成年大小和大部分体积在妊娠中期达到，而此时颞骨和头骨仍在生长。因此，观察到骨迷路与颞骨和头骨之间存在负个体发育异速生长。这与早期研究中观察到的该结构的进化负异速生长相匹配。骨化完成后几乎没有变化；只有开放结构（即耳蜗导水管和内淋巴囊）在出生后继续生长，并反映出颞骨大小的增加。
