Maxillary vertically erectile, perpendicularly to ectoptery goid, and reaching quadrate or mandible: Viperidae.
The maxillary palps have usually three, the labial either two or four segments.
The palps, both maxillary and labial, have two segments.
Maxillary and labial palpi are also present, and the latter, together with the labrum or lower lip, form the rostrum.
The premaxilla is always unpaired, but each half has three long processes directed backwards; one fuses with the maxillary bone, another helps to form the anterior part of the palate, while the third, together with its fellow, forms the " culmen " and extends backwards to the frontals, or rather to the ethmoid which there crops up on the surface.