The Cranial Nerve Components of Petromyzon. 177 
The Eyes, the Eye-muscles and their Nerves. 
The eyes are very poorly developed. The retina appears as a 
eup-shaped structure whose edges are folded in until the cavity is 
nearly obliterated. This is apparently due to the pressure of the 
surrounding organs, especially the body museles below the eye. 
The dermis is considerably thiekened external to the eyeball and 
the epidermis is somewhat thicker here than elsewhere. From these 
facts it would appear that the function of the eye, if it is used at 
all, in Ammocoetes of this age is very limited. 
The muscles will be deseribed briefly under the names given 
them by the FÜRBRINGERS and KOLTZOFF (26, p. 339 and fol.). The 
-musculus obliquus posterior arises from the caudal wall of the orbit, 
from the fibrous covering of the body muscles, and runs forward 
and somewhat upward to the caudal surface of the eyeball. The 
reetus posterior, reetus inferior and reetus superior arise close toge- 
ther from the caudo-ventro-mesial angle of the orbit opposite the 
point of separation of the profundus and trigeminus ganglia. As 
pointed out by HArscHek (11, p. 149) a part of the velar musele 
comes up in the angle between these two ganglia and has its attach- 
ment to the fibrous membrane bounding the orbit at the same point 
from which these muscles have their origin. The reetus posterior 
is the largest of the three muscles and covers the caudal face of 
the eyeball. The reetus superior spreads up over the mesial face 
of the eyeball and the rectus inferior goes beneath the eyeball well 
toward its lateral border. The two muscles at the front of the eye- 
ball have a common origin in the cephalo-ventro-mesial part of the 
orbit and lie close against one another. The obliquus anterior goes 
to the ventral surface of the eyeball, the recetus anterior to its 
cephalic surface. The muscles seem to be closely similar to those 
of Petromyzon marinus and P. planeri as deseribed by P. FÜRBRINGER 
(9), M. FÜRBRINGER (8), Cornıne (7) and of P. planeri described by 
KoLTZoFr (26). 
The histologieal preservation of the muscles is not good in my 
preparations and hence the nerves can not be followed to their final 
distribution with as much certainty as I could wish. I begin with 
N. III which is largest and most easily followed. In its origin from 
the brain it agrees elosely with that of Zampetra (20, p. 12). The 
nerve passes through the eranium and enters the orbit at its ventro- 
mesial angle between the rectus superior and reetus inferior museles 
