54 Joi'RXAL OF CoMl'AKATn'E NeiKOI.OGV. 



me to do more than mention the position of the external 

 roots. 



First ^ or olfactory nerve. — This nerve arises from the 

 cephalic extremity of the rhinencephalon. 



Second, or optic ne>-ve (Plate V, Figs. 4, 7, 9, 13). — The 

 optic fibres arise from the cephalic end of the optic lobe and 

 pass, in a large bundle, to the chiasm. Here they decussate 

 with corresponding fibres of the opposite side, and, after 



ali-sphenoid, close to, or in common with, its fellow. This nerve forms the retina of 

 the eye., 



3, 4, 6. The oculi-moior, pathetic, abducent, collectively the molor nerves of the eye, 

 supplying the muscles moving the eyeball; 3, to all these muscles, excepting the superior 

 oblique and the external rectus; origin from crura cerebri, base of mesencephalon; 4, to 

 the superior oblique; origin behind the optic lobes, upper surface of metencephalon; 6, to 

 the external rectus (also to the muscle of the third eyelid in birds ; 3, 4, 6, exit from the 

 cranial cavity into the orbital cavity by several small, not constant, foramina near the 

 optic foramen; or by this foramen sometimes all of the nerves which enter the orbit pass 

 out of the brain cavity through one greal hole. 



5. Great trifacial or trigeminal, sensori-molor; feeling, skin of head, moving muscles 

 of jaws; origin (double' from mylencephalon, leaves brain from sides of metencepi alon; 

 sensory root has gasserian ganglion, motor root simple. This root has three divisions, 

 whence its name: 5 a, ophthalmic division, the most distinct; exit from cranial into the 

 orbital cavity above and to the outer side of the optic foramen; grooves orbital wall in 

 passing; r/Z/rtry ganglion; distribution mainly to lachrymal and nasal parts; traceable to 

 end of upper mandible; 5 h, superior iiia.xillary: exit by foramen ovale, in ali sphenoid or 

 between that and the prootic centre; distribution to side of upper jaw; vtecklian ganglion; 

 5 c, inferior maxillary, derived chiefly from motor root; exit same as 5 b; distribution to 

 lower jaw (muscles, substance of bone, integument ; no special sense 'gustatory function); 

 no otic ganglion. 



7. Pacini or portio dura, motor, origin from mylencephalon; enters periotic bone, 

 escapes from ear behind quadrate bone, by what corresponds to stylo-mastoid foramen of 

 mammals; communicates with 5 <: by chordo tympanic nerve, with 9, 10, 12 and sympa- 

 thetic system; distribution to skin muscles and others of lower jaw and tongue, etc. 



8. Auditory or portio mollis, nerve of special sense (hearing); origin with 7; no exit 

 from skull; enters meatus auditorious internus of periotic bone; forms auditory apparatus 

 in labyrinth of ear. 



9. Glosso-pharyngeal, mixed nerve, sensori motor and gustatory taste ; origin mylen- 

 cephalon; exit by foramen in exoccipital bone, behind basitemporal, near lower border 

 of tympanic recess; distribution to muscles and membranes of gullet, throat, tongue, etc. 



10. Pneutiiogastric, sensorimotor; origin and exit next tog; distribution to wind-pipe, 

 lungs, gullet, stomach, heart, etc;, has recurrent laryngeal to vocal organs. 



11. '\:\\e, spinal accessory, sensori-motor; origin upper part of spinal cord: exit 9, 10; 

 distribution to these nerves and to muscles of the neck. 



9, lo, II are intimately connected with one another, and with other nerves, espe- 

 pecially 10 with the sympathetic. The several foramina in a bird's skull, which may be 

 seen in the place indicated at 8 Figs. 69, 70 , are for the divisions of this composite vagu?, 

 or "wandering" nerve of respiration, circulation, digestion, etc.; they represent morpho- 

 logically a. foramen lacerutn posterius between exoccipitals and opisthotic centres. 



12. Hypoglossal, motor nerve of the tongue; origin from mylencephalon; exit by 

 anterior condyloid foramen in front of occipital condyle. 



• Thus the idan of the cranial nerves of birds is nearly Cdinrid'Ht with that of mam- 

 mals. — Prof. Kr.i.iorT Coirs, op. cit., pp. 176-7. 



