SENSE ORGANS OF AMIURUS. 365 
tapering may be observed till the upturned portion of the notochord 
is reached where the cord suddenly loses its cylindrical form and 
dilates into a pyramidal swelling. This is, no doubt, owing to the 
greater size of the ventral as compared with the dorsal columns in 
this region where two pairs of powerful ventral roots are given off 
behind the last dorsal roots. 
Il. PERIPHERAL NERVOUS SYSTEM. 
The intracranial course of the cranial nerves has been described 
at page 355. It remains to follow them to their terminations out- 
side the skull. Nothing further need be said with regard to the 
olfactorius and opticus. 
Owing to the small size of the eyes, the dissection of the motor 
nerves of the eyeball is a matter of some difficulty, which may 
account for the fact that I have not been able to find any trace of 
an oculomotor or ciliary ganglion, although I have examined the 
whole of the third and ciliary nerves within the orbit for that pur- 
pose. 
In the course of passing through the skull the third nerve leaves 
the infero-medial strand of the trigeminus, to enter a special canal in 
its course to the orbit which it reaches between the FR. ophthalmicus 
protundus and the AR. ciliaris. It divides immediately into the 
superior and inferior divisions, the former of which runs at once to 
the rectus superior while the latter crosses obliquely over the rectus 
inferior and medius, supplying them, to end by the long branch in the 
obliquus inferior. 
In dissecting from the floor of the mouth, (Figs. 1, 2, 3, Pl. IV.) the 
rectus externus has to be reflected to expose the inferior division of the 
third taking this course. 
The trochlearis accompanies the 2. ophthalmicus profundus into the 
orbit and leaves it there about the middle of its course to pass 
obliquely forwards and outwards to end in the obliquus superior. In 
its course there, certain fibres from the ophthalmicus may be asso- 
ciated with it (Figs. 4, Pl. IV.) which end in the fat near the superior 
oblique muscle. 
The abducens also leaves the ventral edge of the infero-medial 
strand, and crosses to accompany the third into the orbit ; this it 
does apparently in the same sheath, although it may be readily 
