
No. 465.] STUDIES OF MYXINOIDS. 645 
the other. These two tendons run cephalad to the tooth plate, 
just before reaching which they separate, the outer tendon 
attaching itself to the ventral surface of the tooth plate along 
the median line, the inner one dividing into two which curve 
laterad, run ventrad of the plate, and insert near the lateral. 
border. The fibers of the long muscle are directed longitudi- 
nally. Shortly before reaching the caudal end, they separate 
into two divisions, permitting the passage between them of 
the perpendicular muscle. They curve around this, curve mesad 
toward each other, and end in a thin fascia that forms a partition 
between them. When this long muscle contracts, it draws the 
tooth plate back into the mouth, and then flattens it out again. 
But as the long muscle is fixed only at one end, it cannot con- 
tract without assistance, hence the perpendicular and circular 
muscles. 
The perpendicular muscle (Müller's “innere senkrechte 
Muskel der Zunge”), is a short rather stout muscle, arising 
from a small cartilage on the ventral surface of the *' club," 
and running cephalo-dorsad, where it ends in a bounding fascia 
(Figs. 3, 4, P. m.). This little muscle, surrounded as it is by the 
long muscle, acts as a fixed point for the latter to contract 
around, and by contracting itself, increases its diameter as a 
pillar, and by thus taking up more room, helps the other to con- 
tract. 
The circular muscle, also one of the mandibular muscles 
(Fürbringer's m. copulo-copularis, Müller's *hóhler Aussermus- 
kel der Zunge "), is a hollow cylinder surrounding the long mus- 
cle (Figs. 3, 4, c. m.). It begins about a quarter of an inch caudad 
of the tooth plate, and continues to within half an inch of the 
caudal end of the “club.” It is much thicker at its cephalic 
end, where the long muscle consists of little more than a tendon, 
than at the caudal end, its walls growing thin there, and the long 
muscle increasing in girth. It is covered with an aponeurosis 
into which its fibers are set. Its fibers run circularly at right 
angles to the long axis of the “club.” In cross section the 
walls of the circular muscle are seen to be crescent-shaped, 
thick on the ventral surface and at the sides, but thinning as 
they proceed dorsad, until only a thin layer or fascia is left to 
