Dixon—On the Development of the Branches of the Fifth Cranial Nerve in Man. 27 
forwards and outwards beneath it. To the inner side of the ophthalmic, the third 
nerve passes forwards and downwards, while the fourth nerve lies above it. 
The ophthalmic nerve after a course of 0°32 mm., divides into frontal and nasal 
branches. In the angle between these two the small upper division of the third 
nerve passes outwards and forwards. 
The lower and nasal branch of the ophthalmic at first passes forwards and 
upwards, nearly parallel to the upper or frontal branch. Having crossed the 
optic nerve, the nasal nerve changes its direction, and turns inwards, 
running, at the same time, however, forwards and upwards. At the point where 
the nasal thus suddenly changes its direction, it gives off its infratrochlear 
branch, which, continuing the direction of the first part of the nasal trunk, ends 
near the inner part of the eyeball. This infratrochlear nerve is about 1:0 mm. 
long, and gives off a fine branch which runs downwards, and to the inner side of 
the eyeball. The nasal nerve, running inwards and forwards, and having given 
off its infratrochlear branch, then turns slightly upwards towards the brain, to the 
under surface of which, it comes into close proximity, just to the outer side of 
the olfactory nerves. 
As the floor of the cranium is not marked off at this stage from the tissues below, 
it follows that the nasal nerve has, up to the present, not passed through any very 
compact tissue. The nerve now passes downwards and forwards to a point just 
below the groove at the root of the nose, and here, approaching the surface, the 
nerve traverses denser tissue. ‘The nasal nerve, as it crosses the optic stalk, gives 
off two fine twigs, one of which runs along the outer, the other along the inner 
side of the optic nerve to the eyeball. The nasal nerve, from its origin to its 
termination, is 2°2 mm. in length. 
The lachrymal nerve arises from the ophthalmic at the point where the nasal 
takes origin. This lachrymal is a fine nerve that passes, at first horizontally 
outwards, but afterwards ascends somewhat. It is at first some distance from the 
eyeball, but as it passes outwards it lies close to the equator of the eyeball. 
The lachrymal nerve communicates by a very fine twig with the posterior part 
of the orbital branch of the superior maxillary nerve. No trace of a lachrymal 
gland was detected. The length of the lachrymal nerve is 0-8 mm. 
The frontal nerve is the upper thicker branch of the ophthalmic, and lies 
at its origin between the upper division of the third nerve below and the fourth 
nerve above. It communicates with the fourth nerve by a stout branch. 
The frontal nerve runs upwards and forwards, parallel to the nasal nerve, until 
the latter turns inwards; there also the frontal nerve changes its direction and 
turns outwards, but before it does so it gives off its supratrochlear branches. The 
supratrochlear nerve is represented by two twigs, which rising from the frontal 
where the latter changes its direction, are continued forwards over the eyeball 
TRANS. ROY. DUB. SOC., N.S. VOL, VI., PART II, F 
