THE ANATOMY OF BIRDS. — NEUROLOGY. 
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cavity between centres of orbito-sphenoid and alispbenoid, close to or in common with its 
fellow. This nerve forms the retina of the eye. 3, 4, 6, the oculi-motor, pathetic, abducent, 
collectively the motor nerves of the eye, supplying the muscles moving the eye-ball; 3, to all 
these muscles excepting superior oblique and external rectus ; origin from crura cerebri, base of 
mesencephalon ; 4, to the superior oblique, origin behind optic lobes, upper surface of meten- 
cephalon ; 6, to external rectus (also to muscles of the' third eyelid in birds) ; origin between 
met- and myel-encephalon, base of brain ; 3, 4, 6, exits from cranial into orbital cavity by 
several small, not constant, foramina near optic foramen ; or by this foramen sometimes all the 
nerves which enter the orbit pass out of brain cavity through one great hole. 5, great trifacial 
or trigeminal, sensori-motor ; feeling skin of head, moving muscles of jaws ; origin (double) 
from myelencephalon ; leaves brain from sides of metencephalon ; sensory root has gasserian 
ganglion ; motor root simple. This nerve has three divisions, whence its name : 5a, ophthalmic 
division, the most distinct ; exit from cranial into orbital cavity by separate foramen above 
and to outer side of optic foramen ; grooves orbital wall in passing ; ciliary ganglion ; distri- 
bution mainly to lacrymal and nasal parts ; traceable to end of upper mandible 5b, superior 
maxillary; exit by foramen ovale, in alisphenoid or between that and prootic centre ; distribu- 
tion to side of upper jaw ; meckelian ganglion ; 5c, inferior maxillary, derived chiefly from 
motor root ; exit same as 5b; distribution to lower jaw (muscles, substance of bone, integu- 
ment) ; no special sense (gustatory) function ; no otic ganglion. 7, facial or portio dura, 
motor ; origin from myelencephalon ; enters periotic bone, escapes from ear behind quadrate 
bone, by what corresponds to stylo-mastoid foramen of mammals ; communicates with 5c by 
chorda tympani nerve, with 9, 10, 12, and sympathetic 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 auditorius internus of periotic 
bone; forms auditory apparatus in labyrinth of ear. 9, glosso-pharyngeal, mixed nerve, sensori- 
motor and gustatory (taste) ; origin myelencephalon ; exit by foramen in exoccipital bone, 
behind basitemporal, near lower border of tympanic recess ; distribution to muscles and mem- 
branes of gullet, throat, tongue, etc. 10, pneumogastric, sensori-motor ; origin and exit next 
to 9; distribution to windpipe, lungs, gullet, stomach, heart, etc. ; has recurrent syringeal to 
vocal organs. 11, spinal accessory, sensori-motor ; origin upper part of spinal chord ; exit with 
•9, 10 ; distribution to these nerves and to muscles of neck. 9, 10, 11, are intimately connected 
with one another, and with other nerves, especially 10 with sympathetic. The several fora- 
mina 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 vagus or " wandering " nerve of respiration, circulation, digestion, 
etc. ; they represent morphologically a foramen lacerum posterius, between exoccipital and 
opisthotic centres. 12, hypoglossal, motor nerve of the tongue ; origin from myelencephalon ; 
exit by anterior condyloid foramen in front of the occipital condyle. Thus the plan of the 
■cranial nerves of birds is nearly coincident with that of mammals. 
The Spinal Nerves, in pairs, coiTespond in a general way to the vertebrae, between 
which they pass out by intervertebral foramina, to supply the body at large. They are sensori- 
motor ; arise from the spinal chord by anterior motor and posterior sensory (ganglionated) roots 
which unite before leaving the spinal canal ; in the sacral region the main branches leave by 
separate foramina. They form plexuses or interlacements. The principal of these is the 
brachial plexus; constituted by several lower cervical nerves, and one or two usually counted 
as dorsal, which combine to form a single chord, whence the nerves of the wing are derived. 
Similar network of three to five true sacral nerves furnishes the nerves of the leg. 
The Sympathetic System consists of a pair of nervous chords running lengthwise below 
the bodies of the vertebrae, one on each side in the trunk, and in corresponding relations with 
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