The Connection Between The Muscles And The Dura Mater In The Suboccipital Region Of The Gallus Domesticus

Objective:The suboccipital area is a complex anatomical region.Studies have shown that there exists dense connective tissue bridging the suboccipital muscles and the ligamentum nuchae with the spinal dural mater,this bridging structure is called the "myodural bridge".The posterior atlantooccipital membrane and the spinal dural mater are closely connected by dense fibers from the rectus posterior minor muscle at the atlantooccipital space.Additionally,fibers from the rectus capitis posterior major,the oblique capitis inferior muscles,and the nuchae ligaments also connect to the dura mater.Using gross anatomical and P45 sectional plastination methods,our group has also found the ‘to be named ligament' which is composed of thickened fibers of the nuchae ligament involved in the formation of the myodural bridge.The function and clinical significance of the myodural bridge are speculated but are however been studied by scholars.In the past,scholars have put forward a lot of hypotheses about the function of the myodural bridge.Some researchers inferred that the MDB may play vital physical roles in keeping cervical balance,resisting dural infolding,monitoring dura tension,and protecting cervical injury,Others proposed that the myodural bridge may be involved in translating dural tension,and maintaining the fluency of the subarachnoid spaceOur group also proposed a new view that the myodural bridge is related to cerebrospinal fluid circulation.Traditionally,it has been believed that the power source of cerebrospinal fluid circulation is mainly provided by the arachnoid granules,the respiratory system and the cardiovascular system pulsation.However,our group believes that the myodural bridge is one of the power sources of cerebrospinal fluid circulation.Our hypothesis states that when the head moves,the rectus capitis posterior minor muscle contracts during this movement,the contraction pulls on the spinal dural mater through the myodural bridge,resulting in change in the volume of the subarachnoid space.It produces a negative pressure,similar to the "pump effect",and this will have an effect on the cerebrospinal fluid circulation.This function of the myodural bridge is probably one of the important power sources of cerebrospinal fluid circulation.Vertebrates are animals with vertebrae,a subgroup of chordate animals,including Class Pisces,Avifauna,Amphibians,Reptiles and Mammals.A recent study revealed the existence of the myodural bridge also in five other mammalian taxa,that is,Macaca mulatta,Oryctolagus cuniculus,Canis familiaris,Felis catus,Ratus norvegicus,Cavia porcellus and Indoasian finless porpoise,and hypothesized that it may be widespread among mammals.In addition,it was shown that the posterior occipital muscles insert on the dorsal side of the dura mater of the spinal cord by multiple trabeculae in the Siamese crocodiles,Crocodylus siamensis.However,the existence of myodural bridge in Avifauna has not been reported.The comparative anatomy of vertebrates is to compare the morphological structure and physiological functions of vertebrates on the basis of anatomy,and find out their relationship in phylogeny,this could elucidate the ways and rules of animal's evolution.Since the myodural bridge exists in Mammals and Reptiles,The question : does Avifauna have myodural bridges or myodural bridge-like structures? If it exists,how is it similar or different from mammals and reptiles? If not,why? In this study,Gallus domesticus was selected as representative animals to explore the existence of myodural bridge.Gallus domesticus is a member of galliformes of the pheasant family in Avifauna.It is widely seen in daily life and has flexible neck movement.It can be used as a research object to explore whether the myodural bridge exists in birds.Materials and methods:After anesthesia with chloral hydrate,the 56 Gallus domesticus were treated with formalin perfusion and fixation.45 Gallus domesticus were used to gross anatomical observation,5 Gallus domesticus were devoted to sectional anatomy,and 6 Gallus domesticus was used for the histological analysis.Results:Gross anatomy and sectional section of the suboccipital region of the neck of the Gallus domesticus revealed dense connective tissue fibers connecting the deep surface of the rectus capitis posterior minor to the posterior atlantooccipital membrane.The posterior atlantooccipital membrane and dura membrane are connected by many dense trabecular fibrous structures.The trabecular morphology are of different types,they are: flake-like,cord-like and mesh-like.The H & E Histological staining showed that the dense fibers on the ventral side of the rectus capitis posterior minor fused with the posterior atlantooccipital membrane,and the posterior atlantooccipital membrane sent out trabecular network.Moreover,the trabecular which were emitted from the trabecular network connect with the spinal dura mater through the venous sinus.The results of the Van Gieson special staining and Masson trichrome special staining showed that the trabecular network generated by the posterior atlantooccipital membrane and the trabecular which was sent out by the trabecular network that connected with the spinal dural mater are composed of collagen fibers.Under the polarized light microscope,the result of Picrosirius Red Staining shows that the trabecular fiber which were emitted from the trabecular network was type I collagen fiber,and the trabecular network also be composed of type I collagen fibers.Conclusion:It is the first study to find the existence of tendinous myodural bridge in the Avifauna,which proves that the myodural bridge is a highly evolutionarily conserved structure.It is speculated that the Avifauna myodural bridge provides drive for the cerebrospinal fluid circulation via two aspects: first,during head movement,the myodural bridge may maintain the patency of the occipital venous sinus and pull the venous sinus,thereby promoting the cerebral venous blood reflux,and thus play a role in promoting the cerebrospinal fluid reflux;On the other hand,it is possible to exert the "pump function" by pulling the dural sac on the caudal side of the cerebellomedullary cistern and so provide power for the circulation of the cerebrospinal fluid.