No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 669 
They run downward, backward, and outward, the second muscle 
lying external to the third, and the third external to the fourth, 
and are inserted, the second and third muscles on the cartilag1- 
nous processes on the posterior edges of the second and third 
epibranchials, and the fourth muscle at the distal end of the 
bony portion of the fourth epibranchial, the insertion extend- 
ing sometimes onto the cartilaginous, distal end of the piece. 
In one specimen there was an additional muscle, not found in 
any other dissection. It arose with the fourth levator, apparently 
as a part of that muscle, but wholly distinct from it, and was 
inserted on the proximal end of the fourth epibranchial, instead 
of at its distal end. 
The fifth externus (Lade.V) arises from the extreme end of 
the posterior process of the intercalar and runs downward and 
backward, posterior to and internal to the posterior edge of the 
fourth externus, to the posterior or outer end of the fourth 
arch. It then turns downward over the outer end of that arch 
and that of the fifth, and is inserted by a tendon, often long, 
to the anterior edge of the clavicle at about one third the 
length of that bone. It is found in 4omm. fishes as a part of 
the fourth levator, and is possibly what McMurrich refers to 
as a “few fibres” of that muscle ‘continued toward the degen- 
erate fifth arch.” No muscle similar to it is described by 
Vetter in any of the forms examined by him. It is innervated 
by a separate branch, or by two delicate branches of, the vagus. 
3. Interarcuales Dorsales. 
The muscles of this group are not all entirely differentiated 
one from the other; there can, however, be distinguished three 
obliqui dorsales on each side of the head, two transversi dor- 
sales, an anterior and a posterior one, and a median retractor 
arcuum branchialium. 
a. Obliqui Dorsales. 
The most anterior of the obliqui (Od!, Figs. 52-59, Pls. 
XXXIV and XXXV) arises from the upper surface of the 
third infrapharyngobranchial internal to the insertion of the 
