The mandibular symphysis extends backwards at least to the fifteenth tooth.
(b) Fourth mandibular tooth fitting into a pit in the upper jaw.
The os articulare bears on its inner side the inner mandibular process which serves for the insertion of part of the digastric muscle or opener of the mouth; another portion of this muscle is attached to the os angulare, which frequently forms a FIG.
All of these are to be regarded as primitively post-oral, but in the course of development the mouth moves back to the mandibular segment, so that the first three somitesocular, antennal and intercalary - lie in front of it.
The piercing portions of the latter - representing their inner lobes or laciniaelie median to the mandibular piercers in the natural position of the organs.