400 
on top of the head and below by the mucous membrane of the roof 
of the mouth and pharynx (Fig. 12). On its medial side it is separated 
from the organ of the opposite side by a thin septum, formed partly 
by bone and partly by connective tissue which fills in a large opening 
in the median wall of the skull. Laterally, in addition to numerous 
vessels and nerves, the organ is bounded by the upper part of the 
M. adductor mandibulae, the M. levator arcus palatini and the an- 
terior and posterior divisions of the M. adductor arcus palatini 
(Fig. 12). 
The Eye Muscles. 
The oblique muscles arise cranial to the electric organ and run 
directly to their insertion on the eyeball. The recti muscles, however, 
have been considerably elongated and modified as the result of the 
development of the electric organ in their midst. 
The rectus superior arises by a strong tendon from the skull, 
caudal to the electric organ and a short distance ventromedial to the 
exit of the electric nerve from the expanded otic portion of the skull. 
The tendon of this muscle is split by the electric nerve which passes 
through it (Fig. 13). Dorsal to the electric nerve the rectus superior 
extends craniad to its insertion on the eyeball, and for about two 
thirds of Ahis distance is imbedded in the substance of the electric 
tissue. It comes to the surface, however, a short distance before its 
insertion where it lies between the skin and the electric tissue. 
The rectus externus is the largest of the eye muscles. It arises 
by a long tendon near the median line directly medial to the origin 
of the rectus superior. It then runs ventral to the electric nerve on 
the caudal surface of the electric organ and curves around on to the 
lateral aspect of the organ, where it runs forward to its insertion. 
The rectus internus is situated on the medial aspect of the electric 
organ. It arises by a small tendon from the thin lamina of bone in 
the septum between the two organs, about opposite the caudal third 
of the electric organ and dorsal to the crania] end of the parasphenoid. 
This muscle curves around the craniomedial angle of the electric organ 
near its dorsal surface to reach the eyeball. 
The rectus inferior is very much reduced in size and is more 
intimately connected with the electric organ than are any of the other 
muscles. It arises by a small bundle of muscle fibres from the median 
wall of the skull about 5 mm ventral to the origin of the rectus in- 
ternus. Immediately after its origin, the muscle tapers into a very 
fine tendon which runs obliquely through the center of the electric 
