No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 661 
f. Review and Comparison of the Visceral Arches. 
A complete visceral arch in fishes consists normally, accord- 
ing to generally accepted views, of four pieces or elements: 
a pharyngeal element above, then an epal, a ceratal, and a hypal 
element, in the order named. The four elements or pieces in 
the adult articulate one with the other, and the hypal element 
articulates also at its distal end with a median, ventral line of 
one or more basal elements. 
The arch is always preformed in cartilage and it may persist 
as such in the adult, or one or more of its elements may become 
more or less ossified, the ends of the elements always remain- 
ing cartilaginous even in fishes where the ossification is most 
complete. The bones so preformed in cartilage may receive 
membraneous additions, as the hyomandibular in Amia, and 
the ossification of the cartilage may take place from two or 
more different and apparently independent points or centers, 
as in the ceratohyal of Amia and the hypohyal of Perca and of 
Scomber, the element in such cases presenting, in the adult, 
two or more osseous portions, usually, but perhaps not always, 
separating by an interspace of cartilage. 
The anterior branchial arches always present the most com- 
plete and normal development. In the hyoid and mandibular, 
or palato-mandibular, arches the development is irregular or 
exaggerated, and in the posterior branchial arch it is always 
abbreviated, one or more of the normal elements of the arch 
not being found. In this last arch, and also in the other 
branchial arches that may be incompletely or irregularly devel- 
oped, the ceratobranchial is always found, and the outer, lateral 
angle of the arch, in the adult, is always at the outer, upper 
end of that element, between it and the next preceding element, 
whatever that element may be. The pharyngobranchial is 
probably also always found in all the arches, but it is subject 
to much variation in different species, and also in the different 
arches of the same individual. It may be found as a single 
piece; as a small and unimportant piece detached from the 
other pieces, as is probably the case in the fifth arch of Amia 
and of Scomber ; as a piece with two processes or portions, as 
