618 FUNCTIONS OF THE CEREBRO-SPINAL NERVOUS SYSTEM. 



choroidese. Section or paralysis of the 3d occasions drooping of the upper 

 eyelid (ptosis) ; external strabismus, persistent dilatation of the pupil, and 

 accommodation of the eye for distant objects. The 4th nerve is confined to 

 the Superior Oblique, and the 6th to the External Rectus. The number of 

 fibres in the 3d nerve is about 15,000, in the 4th about 1100, in the 6th from 



FIG. 226. 



The Nerves of the Orbit seen from the outer side: 1. Section of the frontal bone; immediately 

 behind the numeral is the frontal sinus, and, in front, the integument. 2. The superior maxillary 

 bone; the section in front of the numeral exhibits the maxillary siuus. 3. Part of the sphenoid bone. 

 4. The levator palpebne and superior rectus muscles. 5. The superior oblique muscle. 6. The inferior 

 oblique muscle. 7. The ocular half of the external rectus muscle drawn forwards. 8. The orbital half 

 of the external rectus muscle turned downwards. On this muscle the sixth nerve is seen dividing into 

 branches. 9. The inferior rectus muscle. 10. The optic nerve 11. The internal carotid artery emerg- 

 ing from the cavernous sinus. 12. The ophthalmic artery. 13. The third nerve. 14. The branch of 

 the third nerve to the inferior oblique muscle. Between this and the sixth nerve (8) is seen the branch 

 which supplies the inferior rectus; its branch to the ophthalmic ganglion is seen proceeding from the 

 upper side of the trunk of the nerve, at the bottom of the orbit. 15. The fourth nerve. 16. The trunk 

 of the fifth nerve. 17. The Gasserian ganglion. 18. The ophthalmic nerve. 19. The superior maxil- 

 lary nerve. 20. The inferior maxillary nerve. 21. The frontal nerve. 22. Its division into branches 

 to supply the integument of the forehead. 23. The lachrymal nerve. 24. The nasal nerve ; the small 

 nerve seen in the bifurcation of the nasal and frontal nerve, is one of the branches of the upper 

 division of the third nerve. 25. The nasal nerve passing over the internal rectus muscle to the an- 

 terior ethmoidal foramen. 2G. The infra-trochlear nerve. 27. A long ciliary branch of the nasal; 

 another long ciliary branch is seen proceeding from the lower aspect of the nerve. 28. The long root 

 of the ophthalmic ganglion, proceeding from the nasal nerve, and receiving the sympathetic root 

 which joins it at an acute angle. 29. The ophthalmic ganglion, giving oil' from its forepart the short 

 ciliary nerves. 150. The glube of the eye. 



2000 to 2500. 1 The third and fourth nerves present some traces of sensi- 

 bility, which in the former nerve is probably derived from the 5th. Chau- 

 vi-aii- observes that the deep or intra-cerebral portions of the motor nerves 

 are quite incapable of being excited to action by direct stimulation ; though 

 on applying irritation to them at the point where they emerge from the 

 cerebrum, movements can always be induced. The peculiar mode in which 

 those motor nerves ordinarily excite the muscles to action, under the guid- 

 ance of the visual sense, will be considered in the next Section. Although 

 commonly ranked as cephalic nerves, they have no direct connection with 

 the Cerebrum; their real origin being from the upper part of the Spinal 

 oots of the 3d pair may be traced into direct connection with 



Axis. The roots of the 3d pair may 



1 Rosrntlial, De Numero atque Mensura Mit-msc-op. Fibrillarum, Breshui, 1815. 



2 Journal dc hi Physiologic, torn, v, 18G2, p. 272. 



