How can giraffe neck vertebrae and human neck vertebrae be considered homologous structures?

Cervical vertebrae

Seven. Just like a human, they are just much much larger.

giraffes have seven neck vertabrae, just like humans

the vertebrae in the neck is called cervical vertebrae.

There are seven vertebrae in a giraffe's neck, just like humans. Just like humans and most mammals, a giraffe has seven neck bones. But those are really, really BIG bones. see the link for more...