No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 729 
This ligament is found strongly developed in the adult, arising 
from the hind edge of the parietal under the extrascapular. 
The suprascapular lies opposite the second muscle segment, 
and the nerve innervating the lateral sense organ contained in 
it, organ No. 1g infraorbital, lies opposite the outer edge of the 
first intermuscular septum. The pedicle of the suprascapular 
is, at this age, still a ligament, lies opposite the first septum, 
and has its attachment to the skull immediately in front of that 
septum. It may, therefore, be homologous with the ligaments 
that arise from the hind end of the basioccipital and lie in the 
fourth and fifth septa. The upper end of the supraclavicular 
lies opposite the third and fourth segments, and the nerves to 
organs 20 and 21 infraorbital lie opposite the second and third 
septa. 
In the adult the muscle segments (J/s) have not the simple 
arrangement found in young larvae. The attachment of the 
intermuscular septa (27s) to the vertebral column, and the line 
followed by their median, inner edges has already been given. 
Their outer edges do not have such a zigzag course. Starting 
from the mid-dorsal line they run first strongly backward, and 
then curve downward and forward to a point approximately 
in the line of the lateral edge of the skull. There they turn 
backward and downward in a gentle curve, cross the line of 
the lateral-line canal, turn downward and slightly forward to 
the line of the outer ends of the ribs, and then curve gently 
forward and downward toward the mid-ventral line. As they 
cross the lateral line and the line of the outer ends of the ribs 
there is a slight notch or interruption in the line of the curve. 
The septa and segments in front of the first rib are always 
short, and while they cannot strictly be said to be irregular, 
they vary somewhat in different specimens and present a much 
more complicated arrangement than the posterior segments. 
Ventral to a radial, longitudinal plane passing, approximately, 
through the line of the lateral edge of the skull, the septa 
and muscle segments incline regularly outward and backward, 
their outer ends lying posterior to the inner ones. Above that 
plane they are not so regularly arranged. The septa in the 
middle point of the muscle mass so defined have been pulled 
