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Bone Begins to Form in Association With the Brain – Skull and Brain Development

by John McLachlan, PhD
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    00:00 Now, in addition, there is a great deal of bone that’s associated with the brain, as you’ll be aware from the study of an adult human skull. The image marked A shows a diagrammatic view of a very simple early version.

    00:15 What we can see is that these structures will form the base of the skull which supports the brain from underneath. And these are quite complex in nature. Some of them were associated with sensory organs. So the trabeculae cranii were associated with the nasal apparatus, the ala orbitalis with the development of the eye, and the periotic cartilage with the development of the inner ear. But as these structures come together, they will begin to fuse.

    00:45 It is a general rule of bone development, but it’s difficult to make a complex structure from a single bone, and therefore, the developmental strategy, if you wish to make a complicated bone, is to take a number of different components and fuse them altogether. In image B, we can see all of these elements beginning to fuse together to form the base of the skull.

    01:10 We can imagine looking at this image from the side. Here we can see marked in dark green, the images we’ve just been looking at from above. We can see how they are coming together to form the base of the skull. Of course, the largest part of the skull is the dermal bony place which will also form an association, but separately. The base of the skull is formed from cartilaginous precursors which then become bone, which then ossify. But the bony plates of the skull forming the vault of the skull come from dermal bone, which differentiates directly in the mesoderm. You can see that it forms from different centers. Here we see the frontal bone and the parietal bone, and these centers will expand towards each other.

    01:56 But in the early stages, there will be significant gaps between those, and those gaps do not fully disappear until significantly after birth. In this image, we can see these bones moving towards each other. Gradually, they will begin to lock and fuse until finally the skull looks as if it really only has two major components, the base locked to the vault, and the jaw as being one separate component. This is a computerized tomography image of the skull of an 18-week foetus seen from above. We can see the bony plates and they are rather rough edges at this stage, and also the gaps in between them through which we can see through to the base of the skull. In the second image, the bony plates of the skull had been removed and we’re now looking at the complexity of the base of the skull. If we look at this inside in frontal views, we can see that the bony plates are far from complete, and there are still major gaps between them. And the other components are gradually beginning to come together to fuse and finally lock to form the adult skull as we recognize it.


    About the Lecture

    The lecture Bone Begins to Form in Association With the Brain – Skull and Brain Development by John McLachlan, PhD is from the course System-Specific Embryology with John McLachlan.


    Author of lecture Bone Begins to Form in Association With the Brain – Skull and Brain Development

     John McLachlan, PhD

    John McLachlan, PhD


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