668 ALLIS. (Vo. XII. 
tores and beyond the vagus foramen to the posterior surface of 
the slight elevation representing, in Amia, the bulla acustica. 
There are, in the adult, seven levatores on each side of the 
head : two interni, an anterior and a posterior one; four externi, 
one to each of the first four arches ; and a fifth muscle, which is 
inserted on the clavicle instead of on the branchial arches, and 
hence can be considered as one of this group of muscles simply 
because of its origin with, or even as a part of, the fourth 
externus. 
The anterior internus (Laéz*) is, both at its origin and at its 
insertion, the anterior muscle of the group. It runs median- 
ward, downward, and forward across the posterior part of the 
bulla acustica, external to the glossopharyngeus, the vagus, and 
the efferent artery of the first arch, and is inserted partly on the 
bone and partly on the cartilage of the proximal end of the 
second infrapharyngobranchial. It is innervated by a branch 
of the glossopharyngeus. 
The posterior internus (Za@éz%) arises external to the poste- 
rior portion of the anterior muscle. It runs downward, median- 
ward, and backward external to the vagus, and is inserted on 
the upper surface of the third infrapharyngobranchial, near the 
middle of the piece, the insertion being partly on the hind edge 
of the bony portion of the piece and partly on the cartilage 
adjoining it. 
The first externus, or levator arc. branch. ext. ad arcum pri- 
mum (Laée./), the externus anterior of McMurrich, is a short 
muscle arising immediately external to the anterior internus, 
and running almost directly downward to its insertion on the 
posterior edge of the first epibranchial, at the proximal end of 
the bony portion of the piece. In one specimen the anterior 
fibres of the muscle had separated as a small separate bundle. 
The second, third, and fourth externi (Lade.//-/V) arise 
close together, almost as a single muscle, the surface of origin 
lying immediately behind that of the first externus and imme- 
diately external to that of the posterior internus. They are 
found in 40 mm. specimens as partly separated portions of a 
single muscle, are considered by McMurrich as such in the 
adult, and are called collectively by him the externus posterior. 
