No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 657 
sions are continued across the cartilaginous interspace, one 
passing dorsal to and behind the articulation with the epihyal, 
and the other ventral to and in front of it. The upper end of 
the bone is capped with cartilage, and articulates with the side 
of the skull in a deep facet lying immediately under its over- 
hanging upper, outer edge and extending forward, downward, 
and inward from its posterior, outer corner to the hind edge of 
the postorbital process. The facet is deepest at its anterior 
end, and there lies immediately behind the spiracular canal. 
The anterior edge of the hyomandibular, in front of the facial 
canal, is thin, and is, as van Wijhe concluded (No. 129, p. 269), 
of secondary origin, for even in fishes 40mm. in length it is 
found as membrane only. The facial canal, however, lies 
entirely in that portion of the bone that is of cartilaginous 
origin, and in the smallest specimens examined, those 12 mm. 
in length, it apparently lay relatively further from the front 
edge of the element than in the older ones. 
The symplectic (SY, Fig. 4, Pl. XX) is an irregularly shaped 
bone directed downward and forward and ending below ina 
large facet lined with cartilage, by which it articulates with 
a large process at the lower end of the hind edge of the 
coronoid process of the mandible, the process containing and 
being strengthened by ossicle d of Bridge. It lies entirely 
below the hyomandibular, with its upper, posterior edge on a 
level with the corresponding edge of the quadrate, and its 
anterior half covered externally by the posterior and upper 
portion of that bone. A depressed portion on the inner sur- 
face of the quadrate receives the symplectic, and the two bones 
are firmly bound together by tissue. The rest of the symplec- 
tic, excepting only the lower end of its articular head, is cov- 
ered externally by the lower end of the preoperculum, which 
abuts with its front edge against the thickened hind edge of 
the quadrate. Between the three bones, the preoperculum 
and the quadrate externally, and the symplectic internally, a 
space or canal is left through which the mandibular branches 
of the facialis pass. The three bones are firmly bound together 
by tissue, as are also the upper end of the preoperculum and 
the hyomandibular, the former bone crossing, and being closely 
