Zhao Huangfu; Xiao Zhang; Jia-Ying Sui; Qi-Qi Zhao; Xiao-Ying Yuan; Chan Li; Ya-Ru Dou; Wei Tang; Mei-Ling Du; Nan Zheng; Yan-Yan Chi; Sheng-Bo Yu & Hong-Jin Sui

The myodural bridge (MDB) is confirmed that connecting the most of suboccipital muscles to the cervical dura mater through the posterior intervertebral spaces and widely exists in mammals and birds. In order to reveal whether the MDB is universally existing in amniota of vertebrates, we explored the existence and the morphological features of the MDB in the Trachemys scripta elegans. Twenty fresh red-eared slider specimens were observed by the gross anatomy dissection and histological analysis. In the results, three kind of muscles in the postoccipital region of the red-eared slider were found. The rectus capitis dorsum minor muscle originated from the posterior margin of the occiput (C0) and terminated at the spinous process of the atlas (C1). The transversospinales muscle was attached to the vertebral arch and the postzygapophysis of the atlas and extended to the spinous process of the axis (C2). The C2-C3 intertransversales muscle were extended from the postzygapophysis of C2 and the one of C3. The three muscles covered the dorsal interspaces among C0-C3, and meantime they were closely connected with dense connective tissues, which filled in these interspaces. Each of these thick dense connective tissue membranes sent off several short and strong fibrous bundles ventrally to merge with the cervical spinal dura mater. Furthermore the connective tissues connecting these muscles with cervical spinal dura mater directly were revealed under the microscopy and they consisted of parallel and intensive collagen fibers with orientation from dorsal to ventral. In conclusion, this study for the first time demonstrated the existence of the MDB in the testudines, in all of the dorsal atlantooccipital, atlantoaxial and C2-C3 intervertebral spaces. Based on our results and comparative anatomical evidences in recent year, it could be inferred that the MDB might be its highly conserved structure in the evolution of amniota.

KEY WORDS: Myodural bridge; Trachemys scripta elegans; Amniota; Evolutionary conservation.

HUANGFU, Z.; ZHANG, X.; SUI, J. Y.; ZHAO, Q. Q.; YUAN, X. Y.; LI, C; DOU, Y. R.; TANG, W.; DU, M. L.; ZHENG, N.; CHI, Y. Y.; YU, S. B. & SUI, H. J. Existence of myodural bridge in the Trachemys scripta elegans: Indication of its important physiological function. Int. J. Morphol., 37(4):1353-1360, 2019.