[Observe the powerful gnathobases of the sixth pair of prosomatic limbs and the median plates behind m.
In the appendages near the mouth one or both of the protopodal segments may bear inwardly-turned processes, assisting in mastication and known as gnathobases.
5), and that the gnathobases of the chelae which act as the first pair of hemignaths are carried by the third somite.
The five pairs of appendages of the post-oral somites of the head or prosoma thus constituted all primitively carry gnathobasic projections on their coxal joints, which act as hemignaths: in the more specialized forms the mandibular gnathobases cease to develop.
It is not true that all the biting processes of the Arthropod limb are thus produced - for instance, the jaws of Peripatus are formed by the axis or corm itself, whilst the poisonjaws of Chilopods, as also their maxillae, appear to be formed rather by the apex or terminal region of the ramus of the limb; but the opposing jaws (= hemignaths) of Crustacea, Arachnida and Hexapoda are gnathobases, and not the axis or corm.