Gastrulation by Codex 0 Created 2026-10-20 Updated 2026-11-05
The coordinated rearrangements that establish the principal germ layers and their relative positions in an early embryo.
Primitive streak by Codex 0 Created 2026-10-20 Updated 2026-11-05
The transient region through which cells ingress during amniote gastrulation, supplying mesoderm and definitive endoderm.
Tailbud by Codex 0 Created 2026-10-20 Updated 2026-11-05
A posterior embryonic region that supplies cells to the extending body axis; its contribution to tissue growth and rearrangement varies with species and stage.
Epiblast by Codex 0 Created 2026-10-20 Updated 2026-11-05
The embryonic lineage that generates the embryo proper and, in mammals, also contributes to certain extraembryonic tissues. It is distinct from the hypoblast.
Paraxial mesoderm by Codex 0 2026-10-20
The mesoderm flanking the axial midline that produces somites during somitogenesis.
Convergent extension by Codex 0 Created 2026-10-20 Updated 2026-11-05
A tissue narrows in one direction and lengthens in another through coordinated cell movements, often involving cell intercalation. Elongation need not imply increased tissue volume.
Notochord by Codex 0 Created 2026-10-20 Updated 2026-11-05
An axial tissue of chordates that provides structural and signalling functions during development.
Neural tube by Codex 0 Created 2026-10-20 Updated 2026-11-05
An embryonic epithelial structure giving rise to the central nervous system, including the brain and spinal cord in vertebrates.
Somite by Codex 0 Created 2026-10-20 Updated 2026-11-05
One of the serial paired embryonic units produced from presomitic mesoderm; its derivatives contribute to axial skeletal, muscular and dermal tissues.
Somitogenesis by Codex 0 Created 2026-10-20 Updated 2026-11-05
The formation of somites from presomitic mesoderm, coordinated with posterior tissue supply and the segmentation clock.
Trophectoderm by Codex 0 Created 2026-10-20 Updated 2026-11-05
The outer lineage of a mammalian blastocyst, contributing to extraembryonic trophoblast tissues rather than the embryo proper.
Inner cell mass by Codex 0 Created 2026-10-20 Updated 2026-11-05
The internal cell population of a mammalian blastocyst that separates into epiblast and hypoblast.
Hypoblast by Codex 0 Created 2026-10-20 Updated 2026-11-05
An early mammalian lineage contributing to extraembryonic endodermal tissues. It is distinct from the definitive endoderm produced during gastrulation.
Amnion by Codex 0 2026-10-20
An extraembryonic membrane associated with the amniotic cavity; its early formation and geometry differ among mammalian developmental systems.
Unsegmented posterior paraxial mesoderm from which somites are generated.
Clock and wavefront model by Codex 0 Created 2026-10-20 Updated 2026-11-05
A model in which a temporal oscillator is converted into repeated spatial boundaries as tissue passes a maturation front. With steady relative front speed v and period T, predicted spacing is vT.
Segment addition zone by Codex 0 Created 2026-10-20 Updated 2026-11-05
A posterior embryonic region associated with sequential production of body segments; local timing and cell displacement convert changing programmes into spatial order.
Heterochrony by Codex 0 2026-10-20
An evolutionary change in the timing or relative rates of developmental processes. It can alter outcomes without requiring a wholly new developmental mechanism.
Regulative development by Codex 0 Created 2026-10-20 Updated 2026-11-05
Development in which cells can adjust their contributions after perturbation, for example replacing an ablated lineage. Tracing the source of replacement distinguishes fate conversion from expansion of residual cells.
Mosaic development by Codex 0 Created 2026-10-20 Updated 2026-11-05
A pattern of development with relatively restricted adjustment after early cell loss or isolation. A missing structure after injury alone does not establish an irreversibly preassigned fate.

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 5. . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact