Chan Li; Chen Yue; Bao Yan; Heng-Tao Bi; Heng Wang; Jin Gong; Campbell Gilmore; Heng Yang; Sheng-Bo Yu; Gary D. Hack & Hong-Jin Sui

Myodural bridges (MDB) are anatomical connections between the suboccipital muscles and the cervical dura mater which pass through both the atlanto-occipital and the atlanto-axial interspaces in mammals. In our previous studies, we found that the MDB exists in seven terrestrial mammal species, two marine mammal species, two reptilian species, and one bird species. A recent study suggested that given the “ubiquity” of myodural bridges in terrestrial vertebrates, the MDB may also exist in snakes. Specifically, we focused on the Gloydius shedaoensis, a species of Agkistrodon (pit viper snake) that is only found on Shedao Island, which is in the southeastern sea of Dalian City in China. Six head and neck cadaveric specimens of Gloydius shedaoensis were examined. Three specimens were used for anatomical dissection and the remaining three cadaveric specimens were utilized for histological analysis. The present study confirmed the existence of the MDB in the Gloydius shedaoensis. The snake’s spinalis muscles originated from the posterior edge of the supraoccipital bones and the dorsal facet of the exocciput, and then extended on both sides of the spinous processes of the spine, merging with the semispinalis muscles. On the ventral aspect of this muscular complex, it gave off fibers of the MDB. These MDB fibers twisted around the posterior margin of the exocciput and then passed through the atlanto-occipital interspace, finally terminating on the dura mater. We observed that the MDB also existed in all of the snakes’ intervertebral joints. These same histological findings were also observed in the Gloydius brevicaudus, which was used as a control specimen for the Gloydius shedaoensis. In snakes the spinal canal is longer than that observed in most other animals. Considering the unique locomotive style of snakes, our findings contribute to support the hypothesis that the MDB could modulate cerebrospinal fluid (CSF) pulsations.

KEY WORDS: Comparative anatomy; Myodural Bridge; Gloydius shedaoensis; Cerebrospinal fluid pulsation

LI, C.; YUE, C.; YAN, B.; BI, H. T.; WANG, H.; GONG, J.; GILMORE, C.; YANG, H.; YU, S. B.; HACK, G. D. & SUI, H. J. Identification of the myodural bridge in a venomous snake, the Gloydius shedaoensis: What is the functional significance?. Int. J. Morphol., 40(2):304-313, 2022.