52 ALETELS: VOL. Delt: 
75 
37. The levators of the branchial arches probably arise from 
the first and second interarcuals of selachians. There are, nor- 
mally, two of them to each arch, —an external muscle, inserted 
on the epibranchial of its own arch, in close connection with the 
suprapharyngobranchial of that arch, and an internal muscle, 
inserted on the infrapharyngobranchial of the next following 
arch. As the posterior arches, or the pharyngobranchials of 
those arches, disappeared, the internal levators, or interarcuales 
I, of those arches, seem to have acquired attachment to the 
under surface of the spinal column, and thus to have given 
origin to the retractor arcuum branchialium. 
Interarcuales III of selachians are found, in Amia, as a 
series of dorsal interarcual ligaments. 
38. The four muscles called by McMurrich the second, third, 
fourth, and fifth divisions of the levator arcus palatini are 
probably not parts of that muscle. The second and third of 
these muscles are probably derived from the levator maxillae 
superioris of selachians, or from that muscle and one of the 
spiracle muscles. The fourth and fifth muscles are undoubt- 
edly derived from the muscle called by Vetter, in selachians, 
Addgf. As all four muscles are, in Amia, innervated by branches 
of a single nerve, I have called them the second, first, third, 
and fourth divisions, respectively, of the levator maxillae supe- 
rioris. This name is, however, probably not a proper one for 
the third and fourth muscles. 
The nerve that innervates the muscles was found double in 
one Amia, and it is frequently, if not always, double in sela- 
chians. It arises, both in Amia and in selachians, from the 
truncus maxillaris trigemini, and is sometimes assigned to the 
inferior maxillary nerve and sometimes to the superior maxil- 
lary. The muscles may, therefore, belong in part to one or 
more preoral arches. They apparently belong to the inter- 
arcual, and not to the interbranchial muscles. 
In teleosts these muscles either disappear entirely, are 
entirely absorbed by the adductor mandibulae, or persist as 
what are called special insertions or special divisions of the 
latter muscle. 
39. No interarcuales ventrales are described by Vetter in 

