634 THE NERVOUS SYSTEM. 
nerves, which arise from (2) the olfactory bulb. This again is connected by (3) 
the olfactory tract with the brain, to which it is attached by (4) two roots (Fig. 452). 
The anatomy of the roots, tract, and bulb of the olfactory nerve are described 
elsewhere (pp. 528 and 545). 
The olfactory nerves, about twenty in number, arise from the under surface of 
the olfactory bulb. The fibres are non-medullated. Piercing the cribriform plate 
x Olfactory nerves pi a 
| g Superior nasal nerve Branches of naso-palatine nerve | 
NC \ Inferior nasal nerve 
Olfactory 
herves 
Branches 
= of nasal 
4 \\ nerve 
Branches 
of nasal 
nerve/ 
Fic. 453. —INNERVATION OF THE Nasa Cavity. 
of the ethmoid bone, enveloped in sheaths of dura mater, they are distributed in 
the nasal cavity as the nerves of smell. The fibres form fine plexuses on the upper 
portion of the nasal septum, and to a less 
extent over the outer wall of the nose. 
THE SECOND oR Optic NERVE. 
The optic nerve (n. opticus) arises from 
the brain by means of the optic tract (Fig. 
452). This takes origin from the external » 
and internal geniculate bodies, situated on 
the under surface of the optic thalamus at 
its posterior end, and also from the brachium 
of the upper of the two corpora quadri- 
gemina (vide pp. 510 and 591). The optic 
PULVINAR 
ae tract reaches the base of the brain in the 
eee interval between the crus cerebri and the 
CORK pr hippocampal convolution of the temporal 
eric Ge jy) be SUR lobe. The two optic tracts converge in 
front of the inter-peduncular space, internal 
to the anterior perforated spot and the 
termination of the internal carotid artery, 
to form the optic chiasma or commissure. 
This adheres to the under surface of the 
floor of the third ventricle in front of the 
tuber cinereum, and gives rise at each end 
to the optic nerve. The optic nerve, directed 
outwards and forward, pierces the dura 
mater, and passes from the cranial cavity 
into the orbit through the optic foramen 
in company with the ophthalmic artery. 
In the orbit the nerve is imbedded in the 
Fic. 454.— DIAGRAM OF THE CENTRAL CONNEXIONS fat behind the eye-ball, and is surrounded 
ee aie i Rg by the ocular muscles. It is connected 
with the eyeball at a point one-eighth of an inch on the inner side of the axis of 
the eyeball. After piercing the fibrous and vascular coats, the nerve spreads out 
at the optic disc to form the innermost layer of the retina. In the orbit the nerve 
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