588 ALLIS. [Vox. XII. 
the geniohyoidei of opposite sides are still somewhat united at 
the middle line of the head. In Barbus even this indication of 
an inferior muscle has disappeared, the two geniohyoidei simply 
touching each other in the middle line without any connection 
whatever. In all four fishes the muscle runs forward either 
below or above the intermandibularis, or in Barbus between the 
fibres of that muscle, and is inserted, in all, on the mandible, or 
in the floor of the mouth immediately behind it. 
The inferior hyohyoideus of Amia, and probably only the ante- 
rior or lateral part of that muscle, is represented in Heptanchus, 
Scymnus and Acanthias by the inner, deeper layer that lies inter- 
nal to the posterior part of the anterior division of the ventral 
constrictor. It is still connected at its ventral end in these 
fishes with the general median aponeurosis, but in Galeus and 
Carcharinus this connection has disappeared and the muscle is 
inserted, along the edge of the coraco-mandibularis, in a fascia 
which is most strongly developed along the dorsal, inner surface 
of that muscle. This part of the hyohyoideus is probably repre- 
sented in Acipenser by Css, which is still inserted on the inner 
surface of Cs2, as it is in Heptanchus and Scymnus. In Chi- 
maera it is represented by the hyoideus inferior of Vetter which 
shows a separation into two parts. The anterior part is 
inserted on the lower jaw of its own side, while the other, run- 
ning internal to the coraco-mandibularis between it and the 
coraco-hyoideus, passes beyond the middle line of the head and 
is inserted on the lower jaw of the opposite side of the head, 
overlapping at its insertion the muscle of that side. In Amia 
the lateral part of the inferior portion of the hyohyoideus corre- 
sponds closely in origin and insertion with this muscle in Chi- 
maera. It arises from the ceratohyal immediately beneath and 
distal to the geniohyoideus, and is inserted on the under surface 
of the hypohyal and in the integument of the floor of the mouth 
beyond it, its tendons passing internal to the branchiomandibu- 
laris, between it and the sternohyoideus, and, beyond the middle 
line of the head, overlapping the tendons of the muscle of the 
opposite side and extending toward the inner surface of the 
mandible. If this part only of the muscle in Amia is repre- 
sented by the entire muscle in selachians, Acipenser and Chi- 
