THE ANATOMY OF BIRDS.— NEUROLOGY. 183 



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 ocuU-niotor, 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 fi-om crura cerebri, base of 

 mesencephalon ; 4, to the superior oblique, origin behind optic lobes, upper sui-ftice of meten- 

 <!ephalon ; 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 ca\aty through one great hole. 5, great trifacial 

 or trigeminal, sensori-motor ; feeling skin of head, mo\'ing 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, oplitlialmic 

 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 ; 56, superior 

 maxillary; exit by foramen ovale, in alisphenoid or between that and prootic centre ; distribu- 

 tion to side of upper jaw ; m^ckelian 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 corresjionds to stylo-mastoid foramen of mammals ; communicates with 5c by 

 chorda tympani nerve, with 9, 10, 12, and sympathetic system; distribution to skin-muscles 

 iiud 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, s/jma? accessor?/, 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 tcmgue ; 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 vertebra^, 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 lca\'ing 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 (jf tliree t(j 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 



