The myodural bridges' existence in the sperm whale.

Recent studies have identified that the myodural bridge (MDB) is located between the suboccipital muscles and cervical dura mater in the posterior atlanto-occipital interspace within humans. The myodural bridge has been considered to have a significant role in physiological functions. However, there is little information about the myodural bridge in marine mammals; we conducted this study to investigate and examine the morphology of the myodural bridge in a sperm whale. We also aim to discuss the physiological functions of the myodural bridge. In this study, a 15.1-meter long sperm whale carcass was examined. Multiple methods were conducted to examine the bridges of the sperm whale which included dissection, P45 plastination and histological analysis. This study confirmed the existence of the myodural bridge in the sperm whale and shows there are two types of the bridge in the sperm whale: one type was the occipital-dural bridge (ODB), the other type was the MDB. A large venous plexus was found within the epidural space and this venous plexus is thought to contain a great amount of blood when in deep water and thus the movements of suboccipital muscles could be a unique power source that drives cerebrospinal fluid circulation

The myodural bridges' existence in the sperm whale - Fig 3

<p>A photograph (A) and a model image (B) of the dissected connective bridges showing occiput (occi), the musculus rectus capitis dorsalis minor (RCDmi), the dorsal atlanto-occipital membrane (DAOM), the occipital dural bridge (ODB), the myodural bridge (MDB), and spinal dura mater (SDM). occi, the occiput. RCDmi, the musculus rectus capitis dorsalis minor. DAOM, the dorsal atlanto-occipital membrane. ODB, the occipital dural bridge. MDB, the myodural bridge. SDM, spinal dura mater.</p

The posterolateral view of subocciptal musculature and connective tissue in the atlanto-occipital interspace showing occiput (occi), the musculus rectus capitis dorsalis minor (RCDmi), the dorsal atlanto-occipital membrane (DAOM), atlas (C1) and the the capsule of the atlanto-occipital joint (o.c.). occi, the occiput.

<p>RCDmi, the musculus rectus capitis dorsalis minor. DAOM, the dorsal atlanto-occipital membrane. C1, atlas. o.c., the capsule of the atlanto-occipital joint.</p

The myodural bridges' existence in the sperm whale - Fig 1

<p>A basic sperm whale osteology model highlighting the enlarged skull and short cervical vertebrae (A). A photograph showing occiput (occi), atlas (C1), the fused vertebra (C2), and the atlanto-occipital interspace of the sperm whale (B). 1, scapula. 2, fin bone. 3, cervical vertebrae. occi, the occiput. C1, atlas. C2, the fused vertebra. ☆, the atlanto-occipital interspace.</p

The transverse sectional view of the connective bridges and a model image.

<p>A: P45 sheet plastination slice of the the myodural bridge (MDB). B: P45 plastination slice of the the occipital dural bridge (ODB). C: Hematoxylin-Eosin slice of the the myodural bridge (MDB). D: a model highlighting the the musculus rectus capitis dorsalis minor (RCDmi), the dorsal atlanto-occipital membrane (DAOM), the myodural bridge (MDB), the venous plexus, the dura mater and the spinal nerve. periosteum of occi, periosteum of the occiput. RCDmi, the musculus rectus capitis dorsalis minor. DAOM, the dorsal atlanto-occipital membrane. ODB, the occipital dural bridge. MDB, the myodural bridge. SDM, spinal dura mater. d. dura, the dorsal dura. v. dura, the ventral dura. s. nerve, the spinal nerve. v. plexus, venous plexus. ▲, the fibers of the ODB and MDB.</p