634 A N A T 
of the retina, by too firong liglit, may produce fneezing, 
as if a fijmulus had been applied to the membrane of the 
nofe itfelf; why prefling the internal canthus of the orbit 
fometimes (tops fneezing ; why irritation of the nofe or of 
.the eye caufes the eye-lids to Unit convulfively, and make 
the tears to flow plentifully; and why medicines put into 
the nofe do great fervice in difeafes of the eyes. In the 
megrim, all the branches of the -nerves dif’cover them- 
lelves to be affebted: for the forehead is racked with pain; 
the eye-ball is pained, and feels as if it was fqueezed ; the 
.eye-lids fliut convulfively, and make the tears trickle 
down, and an uneafy heat is felt in the nofe. Hence we 
can uqderftand, where external medicines will have the 
heft eii’eft when applied to remove this difeafe, to wit, to 
the membrane of the nofe, and to the forehead ; why al¬ 
ternate preflure near the fuperciliary hole of the frontal 
bone, or fneezing, fometimes gives immediate relief in 
the megrim ; why the fight may be loft by an injury done 
to the fupra-orbitar branch; and how it may be reftored 
by agitation of that branch of this nerve. The fecond 
branch of the fifth pair of nerves may be called viaxillaris 
juperior , from its ferving principally the parts of the up¬ 
per jaw. It goes out at the round hole of the fphenoid 
bone, and fends immediately one branch into the channel 
in the top of the antrum maxillare; the membrane of 
v. hich and the upper teeth areffupplied by it in its paffkge ; 
as are likewife the cheek, upper lip, and noftril. Hence 
a pain in the teeth of the upper jaw occafions a gnawing 
pain deep-feated in the bones of the face, with fwelling 
in the eye-lids, cheek, nofe, and upper lip; and, on the 
other hand, an inflammation in thefe parts, or a megrim, 
is often attended with a fliarp pain in the teeth. Hence, 
an obftruftion in the du6t of the maxillary finus, which 
obliges the liquor fecreted there to find out a preternatu¬ 
ral route for itfelf, may be occafioned by the pain ot the 
teeth. Hence, the upper lip often fuffers when the pa¬ 
late or nofe is ulcerated. The third, or viaxillaris inferior, 
branch of the fifth pair going out of the oval hole of the 
fpheu-oid bone, ferves the mufcles of the lower jaw, and 
the mufcles fituated_ between the os hyoides and jaw. All 
the falivary glands, the amygdalae, and- the external ear, 
have branches from it. It has a large branch loft in the 
tongue, and fends another through the canal in the fub- 
ftance of the lower jaw, to ferve all the teeth there, and 
to come out at the hole in the fore-part of the jaw, to be 
loft in the chin and under-lip. Hence a convulfive con- 
trabiion of the mufcles of the lower jaw, or the mouth’s 
being involuntarily fliut, a great flow of fpittle or l'aliva- 
tion, a pain in the ear, efpedally in deglutition, and a 
fwelling ail about the throat, are natural confequences of 
a violent irritation of the nerves of the lower teeth in the 
tooth-ach ; and pain in the teeth and ear is as natural a 
eonfequence of an angina. Hence.alternate preflure on 
the chin may fometimes relieve the violence of a tooth- 
ach. Hence deftroying the nerves of a tooth by aftual or 
potential cauteries, or pulling out a carious tooth, fo often 
removes immediately all thefe fymptoms. Hence no cure 
is to be found for fome ulcers in the upper or lower jaw, 
but by drawing a tooth. Hence in cancers of the upper- 
lip, the falivary glands are in danger of being affected, 
or the difeafe may be occafioned in the lip by its begin¬ 
ning in the glands. 
'Yhdjixih pair, which is the fmalleft except the fourth, 
rife's from the fore-part of the corpora pyramidalis; and 
each, entering the dura mater behind the.pofterior clinoid 
procefs of the fphenoid bone, has a long courfe below 
that membrane, and within the reccptaculum at the fide 
of the fella turcica, where it is immerfed in the blood 
of the receptacle. It goes afterwards,out at the foramen 
lacerum into the orbit, to ferve the abductor mufcle of 
the eye. A defect in this nerve may therefore be one 
caufe of ftrabifmus. In the paffage of this nerve below 
the dura ranter, it lies very contiguous to the internal ca¬ 
rotid artery, and to the ophthalmic branch of the fifth 
pair of nerves. At the place where the fixth pair is con- 
O M Y. 
tiguous to the carotid, a nerve either goes from each of 
them in an uncommon way, to wit, with the angle beyond 
where it riles obtufe, to defeend with the artery, and to 
form the beginning of the intercoftal nerve, according to 
the common defeription ; or, according to other authors, 
this nerve comes up front the great ganglion of the inter¬ 
coftal, to be joined to the fixth here. 
The feventh pair comes out from the lateral part of the 
annular procefs, behind where the medullary procefles of 
the cerebellum is joined to that tuber; and each being ac¬ 
companied with a larger artery than mod other nerves, 
enters the internal meatus auditorius, where the two large 
bundles of fibres, of which it appeared to coniift within 
the lkull, foon feparate from each other : one of them en¬ 
tering by fevcral fmall holes into the veftibule, cochlea, 
and lemicircular canals, is ftretched on this inner camera 
of the ear in a very foft pulpy fubftance; and being never 
feen in the form of a firm cord, fuch as the other parcei' 
of this and molt other nerves become, is called the portio 
mollis of the auditory nerve. The other part erodes the 
cavity of the tympanum, -where it has the name of chor¬ 
da tympani. It alfo pierces through the parotid gland, 
and divides into a great many branches, which are dil- 
perfed im the mufcles and teguments that cover all the 
fide of the upper part of the neck, the whole face and 
cranium, as far back as the temples, including a confide- 
rable part of the external ear. Its branches having thus 
a confiderable connection with all the three branches of 
the fifth pair, and with the fecond cervicalj occafton a 
confiderable fympathy of thefe nerves with it. Hence in 
the tooth-ach, the pain is fometimes very little in the af¬ 
fected tooth, compared to what it is all along the fide of 
the head and in the ear. Hence probably the relief of 
the tooth-ach from blifters applied behind or before the 
ear, or by a hot iron touching the antihelix of the ear. 
By this communication or connection pollibly too it is, 
that a vibrating firing held between one’s teeth, gives a 
firong idea of found to the perforr who holds it, which 
no body clfe can perceive'. Perhaps too the diftributloa 
of this nerve occafions the head to be lb quickly turned, 
upon the iruprellion of found on our ears. 
The eighth pair of nerves rife from the lateral bafes of 
the corpora olivaria in feparated fibres ; and, as they are 
entering the anterior internal part of the holes common 
to the os occipitis and temporum, each is joined by a nerve 
which afeends within the dura mater from the tenth of the 
head, the firft, lecond, and inferior, cervical nerves: 
this has the name ot the nervus accejforius. The eighth 
pair gives nerves to the tongue, larynx, pharynx, and 
ganglion of the intercoftal nerve; and, being disjoined 
from the ninth and intercoftal, runs ftraight down the 
neck behind the internal jugular vein, and at the external 
llde of the carotid artery. As it is about to'enter the tho¬ 
rax, a large nerve goes off from each (ide : the branch of 
the right fide turns round from the fore to the back part 
of the fubclavian artery, while the branch of the left fide 
turns round the great curve of the aorta; and both of 
tfiem mounting up again at the fide of the cefophagus, to 
which they give branches, are loft at laft in the larynx. 
Thefe are called the recurrent nerves, which we are delired 
to fnun in the operation of bronchotomy. The mufcles 
of the larynx being in a good meafure fupplied with 
nerves from the recurrents, it is to be expebled, that the 
cutting of them will greatly weaken the voice, though it 
will not be entirely loft fo long as the fuperior branches of 
the eighth pair are entire. The recurrents themfelves 
often lend off fmall perves to the pericardium, and to 
join with the branches of the intercoftals that are diftri- 
buted to the heart. After thefe branches are fent off, 
the par vagum on each llde delcends behind the great 
branch of the trachea, and gives numerous filaments to 
the lungs, and fome to the heart in going to the oefopha- 
gus. The one of the left fide running on the fore-part 
of the cefophagus, communicates by feveral branches 
with the right one in its dement to be diftributed to the 
stomach. 
