116 
bulbus has no direct connection with its nerve in front as 
on the right side, nor does it extend as far forwards as the 
right one. There is much more difference in the size of 
the two olfactory nerves than one would expect from the 
sizes of their bulbs; the left being only } the size of the 
right. Nor do its fibres take such an intense stain with 
the osmic acid. For some distance the two olfactory 
nerves course together, but finally the left separates from 
the right and passes upwards towards the eyeless side of 
the body. It then traverses the olfactory foramen in the 
left prefrontal, and at once passes straight upwards to 
break up in the olfactory lamine of the left nasal 
chamber. The left nasal organ is much smaller than the 
right (cp. fig. 25, n. olf., n. olf.1), and hence the small left 
nerve. It is also situated somewhat behind the right, and 
therefore the left olfactory is the shorter of the two. 
Nervus Opticus—ll. 
As in all lower vertebrates, the fibres of the optic 
nerve arise mostly from the roof of the mid-brain (tectum 
opticum), and as is usual in Teleosts they pass forwards 
over the ventricle to collect at the anterior extremity of 
the optic lobe, and then course sharply downwards and 
forwards to reach the surface of the brain. The optic 
chiasma is a simple crossing without any intermingling of 
fibres, so that the nerve to the right eye, for example, arises 
exclusively from the left side of the brain. As in Menzdia 
the nerve to the left eye is uppermost at the crossing. 
Kach optic nerve, as is usual in Teleosts, consists of a thin 
wide ribbon so thrown into longitudinal folds as to form 
a round nerve, and each exhibits 3} folds.* If the optic 
nerve could be flattened out the width of the ribbon would 
“The number of the folds increases with the size of the nerve, judging 
from our sections of young plaice at different stages, and also from the 
condition in the adult (see fig. 28). 
