In skeletal drawings, chemists usually omit hydrogens bonded to carbon; heteroatoms and their attached hydrogens are normally shown. A skeletal structure shows carbon skeletons as zig-zag lines: every vertex and every line-end is a carbon, and each carbon silently carries as many hydrogens as it needs to reach four bonds.

It looks like information has been thrown away. It has not — the hydrogens are recoverable exactly, which is why the convention works.