No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 615 
g. Truncus Hyoideo-Mandibularis Facialis. 
The large truncus hyoideo-mandibularis facialis (4m) arises, 
in 35 mm. specimens, from the ventral, outer, and hinder part of 
the trigemino-facial ganglion. It runs forward and outward, 
then outward, and finally outward and backward through the 
large facial foramen which lies in the petrosal near the front 
edge of that bone and a little behind the lateral wing of the 
parasphenoid. 
In the adult the truncus arises from the lateral surface of its 
ganglion, nearly at right angles to that ganglion and to the line 
of its posterior root. It runs directly outward, or outward and 
backward, through its foramen, and then slightly upward along 
the upper surface of the adductor hyomandibularis, where it 
sends a large branch, the r. opercularis facialis (of7f) backward 
and upward along the upper surface of the adductor hyoman- 
dibularis, and beyond it onto the outer surfaces of the adductor 
and levator operculi, all three muscles being supplied by the 
nerve. After the nerve reaches the outer surface of the 
adductor operculi it breaks up into numerous branches, which 
spread out over the surfaces of that muscle and the levator 
operculi, lying immediately internal to a similar network of 
branches belonging to the glossopharyngeus and first vagus 
nervus and destined to supply the cutaneous and subcutaneous 
tissues of the operculum. 
The r. opercularis facialis, on the left side of the fish used 
for this dissection (Fig. 25, Pl. XXV), was easily separated 
from the truncus facialis as a thin, flat layer closely applied to 
the posterior surface of that nerve, the layer separating even 
beyond the ganglion onto the main root of the nerve, and being 
connected distally by fibres with the main truncus. 
After giving off the r. opercularis the truncus turns down- 
ward, and running downward, outward, and backward, somewhat 
imbedded in the fibres of the adductor hyomandibularis, enters 
and passes through the facial canal in the hyomandibular (/, 
Figs. 1, 2, and 5, Pl. XX). After issuing from that canal the 
truncus facialis continues downward, outward, and backward, 
lying in the depression described on page 000 on the outer 
