No. 3-| MUSCLES AND NERVES IN AMIA CALVA. 561 
in Fig. 43. The fibres of the deeper muscle immediately lat- 
eral to the median bundle pass forward beyond the hind edge 
of the superficial muscle, dorsal to it, and have their insertion 
on the median aponeurosis, or on the hind edge of the inter- 
mandibularis. The fibres lying still more toward the lateral 
edge of the deeper muscle become tendinous, after passing dor- 
sal to the superficial muscle, and are continued beyond that 
muscle, dorsal to the intermandibularis, as a sheet or series of 
flat tendons which lie immediately beneath the integumental 
lining of the floor of the mouth. They are closely attached to 
that integument, and have their insertion partly in it, and partly 
on the inner surface of the mandible near the symphysis. The 
extreme lateral fibres of the muscle run almost directly forward, 
from their origin on the ceratohyal, parallel to the ramus of the 
mandible, and have their insertion in the integument of the floor 
of the mouth along the median edge of the tough layer or fold 
of dermal tissue that extends from the lateral edge of the 
muscle downward and medianward to the lower, inner edge 
of the mandible. Some of the fibres of the muscle are also 
often inserted along the dermal rim formed at the middle of 
the lateral edge of the gular plate. 
The superficial, inferior portion of the geniohyoideus arises, 
in young specimens, in a narrow horizontal line from an exposed 
portion of Meckel’s cartilage on the inner surface of the man- 
dible immediately below the lower edge of the splenial and 
between that bone and the dentary (Fig. 6, Pl. XX). In full- 
grown fishes the surface of origin includes also the edge of the 
dentary immediately below this cartilage. The line of origin 
extends approximately from the hind edge of the intermandib- 
ularis to the level of the front end of the mandibular portion 
of the adductor mandibulae ; that is, through about one quarter 
of the length of the mandible. The muscle is flat and broad 
and runs backward and inward from its origin to the middle 
line of the head, where it is inserted, with its fellow of the oppo- 
site side, on the median, vertical aponeurosis common to it and 
to the deeper portion of the muscle. Its insertion is below, or 
superficial to, that of the deeper portion, and only extends back 
to the point under the middle of the gular plate where, as 
