No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 659 
three bones are bound tightly together by connective tissue, 
extend nearly the entire length of the preoperculum, and form 
the upper portion or piece of the gill cover. The operculum 
articulates, by a large facet on its inner surface, with the end 
of the opercular process or the hyomandibular. The facet is not 
lined with cartilage, and even in the youngest larvae examined 
there is not the slightest indication of cartilage at or in any 
part or portion of the bone. The bone in Amia is strictly of 
dermal origin. 
The suboperculum is attached by ligament to, but does not 
articulate by facet with, the lower, posterior, cartilaginous corner 
of the hyomandibular; and the interoperculum is attached by 
strong connective tissue to the upper end of the upper ossifi- 
cation of the ceratohyal. The interoperculum is also attached 
by ligament (4mz) and by strong, tough, dermal tissue to ossicle 
a, and to the hind corner of the mandible immediately external 
to the insertion of the ligamentum mandibulo-hyoideum. The 
operculum overlaps considerably at its lower edge the upper 
edge of the suboperculum, and the latter overlaps slightly the 
interoperculum. 
The first branchiostegal ray (BRG) extends from the lower 
end of the interoperculum almost to the upper, posterior end of 
the suboperculum. It is overlapped by both these bones and 
is strongly attached by connective tissue to their under surface. 
It is also attached by strong connective tissue to the upper ossi- 
fication of the ceratohyal, near its lower edge, and by strong, 
tough, dermal tissue to the hind end of the mandible. The 
hyoideo-mandibular fold or crease extends upward and _ back- 
ward between it and the second ray, so that on the undissected 
head the first ray has more the appearance of belonging to the 
opercular bones than to the branchiostegal rays. The next 
following rays (indicated in Fig. 43, Pl. XXXI) are loosely 
attached to the outer surface of the lower ossification of the 
ceratohyal, near its hind edge, the most anterior or distal rays 
lying beyond the edge of the ceratohyal upon the outer surface 
of the hyohyoideus. There are usually ten or eleven rays in all, 
and in none of the larval stage examined was there the slightest 
indication of cartilage, either in them or connected with them. 
