THE CRANIAL NERVES AND SPECIAL SENSE ORGANS 87 
be seen anterior to the edge of the diaphragma sellae, and upon 
either side of this stalk the cut ends of the carotid arteries appear. 
Note the relation of the folds of the tentorium to the lateral 
boundaries of the diaphragma sellae. 
By reference to the previous study of the ventral surface of the 
brain, identify the cut ends of the cranial nerves which pass 
through the dura mater to reach their respective foramina of exit 
from the cranial cavity. Draw this view of the floor of the cavity, 
showing these features. 
Make sure of the identification of the optic, oculomotor, troch¬ 
lear, abducent, and ophthalmic branches of the trigeminal nerve. 
With a very sharp scalpel or curved seeker carefully cut 
through the dura mater to trace each nerve forward to its place of 
exit from the cranial cavity into the orbital fossa. The optic 
nerve takes a very short course to reach the optic foramen. The 
trochlear nerve takes a very oblique course through the dura along 
the medial surface of the tentorial fold, which must therefore be 
dissected away from the nerve with great care not to cut or break 
the nerve itself. The abducent nerve passes through the exten¬ 
sive cavernous sinus which lies in the sella turcica lateral to the 
hypophysis, so that to follow the nerve through this sinus involves 
the removal of the spongy structure and clotted blood which fill it. 
The ganglion of the trigeminal nerve (the semi-lunar or Gasserian 
ganglion) lies beneath the fold of the tentorium lateral to the 
cavernous sinus. Follow the ophthalmic branches of this nerve 
forward to the place where, in company with the trochlear, 
oculomotor, and abducent, they pass through the superior orbital 
fissure into the orbital fossa. With these nerves traced, the 
removal of the remaining portion of the dura mater may be 
accomplished without injury to the various nerve roots all of 
which should be left intact. Draw the bony floor of the cavity 
with the dura removed, showing the relation of the various cranial 
nerves to their foramina of exit. 
C. THE EYE AND THE NERVE DISTRIBUTION TO IT. 
(Cf. model of human eye.) 
Taking care not to injure or lose the identity of the nerves 
which have been traced to their entrance into the orbital fossa, 
