THE ANATOMY OF LIRDS.— NEUROLOGY. 177 
cavity between centres of orbito-sphenoid and alisphenoid, 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 
mawillary ; exit by foramen ovale, in alisphenoid or between that and proétic centre ; distribu- 
tion to side of upper jaw; meckelian ganglion; 5c, inferior maxillary, derived chiefly from 
motor root; exit same as 5); distribution to lower jaw (muscles, substance of bone, integu- 
ment); no special sense (gustatory) function; no otie 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 5¢ 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, ete. 10, pnewmogastric, sensori-motor ; origin and exit next 
to 9; distribution to windpipe, lungs, gullet, stomach, heart, ete. ; 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, 
ete.; 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, correspond in a general way to the vertebree, 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 vertebree, one on each side in the trunk, and in corresponding relations with 
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