Occipital-Dural Muscle: A Specialized Myodural Bridge in Narrow-Ridge Finless Porpoise (Neophocaena Asiaorientalis)

A dense bridge-like tissue named the myodural bridge (MDB) connecting the suboccipital muscles and the spinal dura mater was originally discovered in humans. Recent studies have revealed that the MDB confirmed a universal existing normal anatomical structure in mammals which is considered being significant in physiological functions. Our previous investigations have confirmed the existence of MDB in the finless porpoises. We conduct this research to expound the specificity of the MDB in Neophocana asiaeorientalis (N.asiaeorientalis). Five carcasses of N.asiaeorientalis with formalin fixation were used for this study. Two were used for head and neck CT scanning, three-dimensional reconstruction, and dissection of suboccipital region. One was used for P45 plastinated sheets observation. One was for histological analysis of suboccipital region. One was for Scanning electron microscopic study. The results showed that the MDB in N.asiaeorientalis is an independent muscle originated from the caudal border of occiput, directly extended through the posterior atlanto-occipital interspace and connected with the cervical spinal dura mater. Thus the MDB in N.asiaeorientalis is an independent and specialized muscle. Based on the origin and termination of this muscle, we could name it as ‘Occipital-Dural Muscle’. And the direct pull on the cervical spinal dura mater might affect the circulation of the cerebrospinal fluid (CSF) by altering the volume of subarachnoid space of spine.