914 THE AMERICAN NATURALIST. [VoL XXXIX. 
drical tendon. This tendon continues forward, passing outside 
the spiracle and the eye and over the various jaw muscles and 
the antorbital cartilage, into the fascia of the rostral region 
where it is inserted in the strong membranous tissue stretching 
between the rostrum and the propterygium. 
Depressor Rostri. 
The depressor rostri (Fig. 15, Dr), the antagonist of the last, 
is a broad, flat, thin muscle arising from the fascia covering the 
coraco-mandibularis and from the fibers of the coraco-arcualis 
communis. The muscle extends forward and outward in the 
direction of the adductor muscles where some of the lateral 
fibers are inserted in the white fascia covering these muscles,! 
while the majority are collected into a strong tendon which 
extends forward, lateral to the nasal capsule and ventral to the 
antorbital process, then coming towards the median line is in- 
serted in the membranous tissue between the tip of the rostral 
cartilage and the propterygium. 
INTERARCUALES. 
Acanthias. 
The interarcuales (Fig. 9) are divided into two systems of 
muscles: one more medial, the other more lateral in position, 
each consisting of four muscles, similar in function, the first of 
the medial system being the subspinalis of Vetter ('74, p. 444). 
Medial System.— The most anterior of the medial interarcu- 
ales has been treated as a distinct muscle, the subspinalis, by 
Vetter but as it agrees closely with the others in function and 
differs only in its origin from the rest, it is here regarded as 
but one of the set. Its origin is from the fascia on the under 
side of the dorsal longitudinal muscles, from the vertebrze near 
the cranium, and from the under side of the cranium itself just 
in front of the foramen magnum. From this broad origin it 
1 [n Raia radiata most of the fibers have this insertion, 
while a small proportion 
are continued into the rostral depressor tendon. 
