The Fetal Skull



hello welcome to the normal childbirth module and we're going to be talking about the fetal skull this morning and I'm going to be using this plastic model of the fetal skull just to show you various aspects of the fetal skull it's really important to meet with we practice and these are these things that we're going to be talking about are the different areas of the fetal skull the different bones that make up the fetal skull the sutures and the fontanel's of the fetal skull so we're going to be looking at the the fetal skull and in which we practice we divide the fetal skull up into three areas these areas are the vault the face and the base and if we look at the front of the fetus skull first the face is where it's the area from between your orbital ridges which is this area here and it extends all the way from downwards to where the corner of the jaw meets our neck line that area there is called the face the base of the fetal skull is if I turn it over slightly is where the skull joins our spinal column and it extends from there to this area here this area here that you can see at the base of this bone here and then the remainder of the fetal skull is called the vault and this area extends from the orbital ridges all the way across right to where it meets the base here in the nape of our neck in midwifery practice it's the vault but it's got the biggest implications for our midwifery practice and the vault actually comprises seven bones these seven bones are if we look at the front here we've got frontal bones and we've got two frontal bones we've got the left and the right frontal bone that's these two bones here coming towards the posterior aspect now we've got two parietal bones and we've got the left and the right parietal bone so if we look ups from the side we've got the frontal bones we've got the two parietal bones here and then if we look at the back of the fetal skull we've got this bone and this bone here is called the occiput the final two bones that make up the vault are the temporal bones and it's just the superior aspect of the temporal bones which make up the vault and it's these these small areas here and again we've got a left and a right temporal bones that's the right temporal bone and then that's the left temporal bone the next thing that we need to know about are the sutures and sutures there actually are their cranial joints which are formed where two bones meet so where the two frontal bones meet here we've got the frontal suture where the two parietal bones meet along here we've got the sagittal suture where the two frontal bones meet the two parietal bones we've got the coronal suture which runs along here and then if we look at the back where the two parietal bones meet the occipital bone we've got the lam boydle suture and suture is a really important part of the enough to me that actually changes during the process of childbirth because it allows it to grieve overlap of the skull bones during the birth process and that's known as molding and that's really important the final thing that we need to look at on the external structure of the fetus skull are fontanel's and fontanel's are where there are areas where two or more sutures meet and in layman's terms we call them the soft spot so we've got two fontanelles of note we've got the lam boydle fontanel which is here so the lambdoidal runs between the occipital bone and the two parietal bones and then we've got the bregma suture with bregma fontanel sorry and the Bragg mahant analysis Theory here that runs between the two frontal bones and the two parietal bones here so now we've learned about the bones the sutures and the fontanelles of the the skull the next thing that we need to think about are the diameters the actual measurements of a fatal skull and we tie this this knowledge and understanding in with the anatomy of the pelvis that we know to help us guide our midwifery practice during normal childbirth and there are six longitudinal diameters of fetal skull that we need to know about and there are two transverse diameters of the fetal skull and the longitudinal diameters go go kind of from here and the transverse go from one side to the other I'm here so the longitudinal diameters that we need to know the first one is the s OB diameter or the sub occipital Bragg Matic diameter and this is nine point five centimeters and this is measured just below the occipital protuberance which is just here to the anterior fontanelle or the anterior of Bragman so that's the opposite opposite own Bragg Matic diameter and that's always nine point five centimeters the next diameter is the sub occipital frontal diameter and this is ten centimeters and this is measured from below the occipital protuberance again to the center of the frontal suture which is here so this is the sub occipital frontal sof diameter which is ten centimeters the next diameter is the occipital frontal diameter and this is eleven point five centimeters and again this is merged from the occipital occipital protuberance which is here to the glabella and the glabella is here the glabella is the same as the midline between the orbital ridges so that's the glabella there and that's the occipital protuberance there and that is eleven point five centimeters the next diameter is the mento vertical diameter which is thirteen and this meshes from the from the point of the chin the chin is called the mentum this bit here is called the mentum so this is from the mentum to the highest point on the vertex which is just here so that's the Mentos vertical diameter and that's thirteen point five centimeters the next one is the sub Mentos vertical diameter the smv which is eleven point five centimeters and this is measured from the point where the chin joins the neck so from here to the highest point on the vertex which is higher so that's the sub Mentos vertex or smv diameter the final diameter longitudinal diameter is the sub mental pragmatic diameter or the SMB diameter which is nine point five centimeters and this is measured from the point where the chin joins the neck which is here to the center of the Bragman which is here so that would be the sub Mentos pragmatical SMB diameter so we've looked at the longitudinal diameters of the fetal skull now we need to look at the transverse diameters of the fetal skull and we've got two transverse diameter so we've got the skull with the head pointing downwards we've got the biparietal diameter which is the diameter between the two parietal eminence issus eminences are where ossification starts on bones and it's usually Petrobras that that it comes out of the bone and so the biparietal diameter is between the two parietal eminences on the parietal bones and that's nine point five centimeters and then the bitemporal diameter is one at the front and that's eight point two centimeters and that's the diameter between the two furthest points of the coronal sutures at the temples so remember this is the coronal suture so it's at their widest point which is at the temple so they're the two transverse diameter

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