606 
lateral one of these two parts ran almost directly backward and up- 
ward to the usual place of insertion of the muscle on the dorsal sur- 
face of the eyeball. A large part of the fibres of the other, mesial 
part of the muscle ran backward, upward, and mesially and were in- 
serted, by tendon, on the ventral surface of the dorsal wall of the orbit, 
mesial to the line of the supraorbital lateral canal. The tendon of 
this part of the muscle passed, in its course, ventral and then mesial 
not only to the nerve that supplies the sense organs of the supra- 
orbital lateral canal, but also to what I take to be that part of the 
ophthalmicus superficialis that supplies the ampulle near the lateral 
edge of the snout. It passed lateral and dorsal to another large branch 
of the ophthalmic nerves 
that ran forward on to the 
top of the snout mesial to 
the above mentioned branch. 
The remaining fibres of 
this mesial half of the muscle 
joined those of the lateral 
half and were inserted with 
them on the eye-ball. Cer- 
tain of the fibre of this, 
communicating, part of the 
muscle arose directly from 
Fig. 1. Top view of left eye 
of Carcharias. Addß part of ad- 
ductor mandibulae muscle. oz ob- 
liquus inferior muscle. os obliquus 
superior muscle. opp ramus oph- 
thalmicus superficialis. re rectus 
externus muscle. zii rectus internus 
muscle. rs rectus superior muscle, 
tr nervus trochlearis. 
the cartilage of the anterior end of the orbit, but a large part of them 
arose in and apparently from the fibres that had their insertion on 
the dorsal wall of the orbit. That part of the muscle that went 
from orbit wall to orbit wall was, naturally, wholly functionless excepting 
as it offered a point of insertion for those fibres that ran from it to 
the eye-ball. 
Both parts of the muscle were innervated by the nervus trochle- 
aris, the branches of which were distributed to it as shown in the 
accompanying cut. 
The nervus trochlearis as it approached, in its outward course 
from its foramen, that branch of the ophthalmic nerves that lay ventro- 
