560 ALLIS. [Vov. XII. 
rounded behind, where, lying in a dermal fold, it overlaps the 
first branchiostegal rays and covers and protects the isthmus. 
It nearly fills the space between the rami of the mandible, but 
is small enough to pass freely up and down between them, when 
the motions of the mouth require it. The external surface of 
the bone has the sculptured markings characteristic of the 
dermal bones in Amia, the ridges proceeding ray-like from a 
higher central point near the middle of the bone. Immediately 
internal to this point there is a dense connective tissue, almost 
cartilaginous in character, in one of the specimens examined ; 
and on a level with it, along the lateral edges of the bone, there 
is a thick, rigid dermis forming a rim projecting upward and 
laterally. The gular bone itself does not give direct insertion 
to any muscle fibres. 
The geniohyoideus has two well-marked portions, a superior, 
deeper one (Gs) and an inferior, superficial one (G/z). The 
deeper portion is the larger, and is a broad, flat, thick muscle, 
thinning out anteriorly, where it lies immediately below the 
integument of the floor of the mouth. It arises from the outer 
under surface of the ceratohyal, behind the origin of the hyo- 
hyoideus. It is, at its origin, V-shaped in outline, the two 
edges of the muscle extending much further back than the 
central portion. The median edge extends as far as the 
eighth or ninth branchiostegal ray, the muscle in this part of 
its course lying close along the bases of the rays. It is directed 
forward and inward, its median fibres meeting those of the 
muscle of the opposite side of the head in a vertical aponeurosis 
which lies in the middle line of the body and extends forward 
to the hind edge of the intermandibularis. The dense connec- 
tive tissue mass under the central point of the gular plate lies 
in or is a part of this aponeurosis, lying near its hind end. It 
gives insertion posteriorly to a part of the most posterior or 
median fibres of the muscle, which fibres form a somewhat 
separate bundle, rising above the rest of the deeper muscle to 
the level of the superficial one, the posterior fibres of which 
also have their insertion here. Posterior to this point the 
fibres of the deeper muscle are more or less continuous with 
those of the opposite side, and sometimes entirely so, as shown 
