164 JULIA WORTHINGTON. 
going to the ventral surfaces of the middle and lateral 
divisions, those of E to the lateral division only (figs. 1 
and 2). 
Interesting questions arise here: (1) What physiological 
significance has this difference in distribution, and (2) what, 
if any, are the differences of connection of these different 
divisions of the glomerular layer with other parts of the 
brain? I hope, in a later paper, to throw some light upon 
at least the last of these questions. 
N. Opticus.—The optic nerve of Bdellostoma is very 
small and delicate, owing to the undeveloped condition of 
the eye, the latter consisting merely of a round, two-layered 
cup. On leaving the eye the nerve runs medio-caudad, 
passing ventrad of r.ophthalmicus V and r. maxillaris 
posterior V, and dorsad of r. maxillaris anterior V and 
r.mandibularis V (fig. 14). It enters the cranium in the 
ventral part of its lateral wall, ranning caudad in the cranial 
wall for -36 mm., and, emerging on the floor of the cranial 
cavity, runs dorso-mediad to enter the ’tween brain on its 
ventral surface as described above. There is no external 
chiasma. 
N. Trigeminus.—This is the greatest of all the cranial 
nerves except the olfactory. It has two roots, a dorsal 
sensory, and a ventral motor. ‘The sensory root is decidedly 
the larger and stronger of the two, and lies cephalad as well 
as dorsad of the motor. Most of the sensory fibres are fine, 
but a few coarser ones are found among them, notably in the 
ophthalmic branch; the motor fibres are coarse and stiff. 
All the fibres are medullated outside the brain. From the 
moment the nerve leaves the brain the ophthalmic fibres can 
be distinguished from those of the maxillo-mandibular trunk. 
They emerge cephalo-mediad of the others, and lie mesial to 
them in the nerve trunk until the ganglion is reached. 
Leaving the medulla at its cephalo-lateral angle (figs. 1 
and 2) the Trigeminus runs cephalo-laterad as a thick fibre 
bundle to the cranial wall, where it breaks up into several 
smaller strands in order to pass through the  sieve-like 
