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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. [ABSTRACT FROM AUTHOR]

The deep suboccipital muscles has been shown to connect the spinal dura mater via dense connective tissue termed the myodural bridge (MDB). The MDB has both physiological and clinical implications. Data on morphological and imaging anatomical parameters of the deep suboccipital muscles are scare. In this study, T2-weighted images of rectus capitis posterior major (RCPma) and obliqus capitis inferior (OCI) of 109 healthy adults were obtained by 0-degree sagittal and 30-degree oblique sagittal continuous MRI scanning of the head and neck of the subjects. Sectional area parameters of the RCPma and the OCI were measured. The 0-degree sagittal section was measured with 5 mm bias from the median sagittal plane, the sectional area of the RCPma was 186.34± 55.02 mm2 on the left, and 202.35± 59.76 mm2 on the right. The sectional area of OCI was 221.72± 68.99 mm2 on the left, and 224.92± 61.34 mm2 on the right; At the section with 30-degree bias from the oblique sagittal plane, the sectional area of RCPma was 183.30± 42.24 mm2 in males, and 133.05± 26.44 mm2 in females. The sectional area of OCI was 254.81± 46.20 mm2 in males, and 167.42± 27.85 mm2 in females. Significant sex difference exists in the sectional areas of the RCPma and OCI, the values of the male subjects were predominantly larger (P < 0.05), however there were no age-related significant difference. The sectional area of RCPma is bilateral asymmetric, the RCPma on the right side is larger than that of the left side (P < 0.05), but the OCI is bilaterally symmetric (P >0.05). The MRI image features, imaging anatomical data and sexual dimorphism of the RCPma and the OCI are presented in this study. This imaging anatomical data will be useful for functional and clinical studies on the RCPma, OCI, and the MDB. [ABSTRACT FROM AUTHOR]