ANATOM Y. 5 6 9 
of the fare, and two concealed by the angle of the jaw. 
1. Tempo '■ atis, arifes from a femicircular ridge of the low¬ 
er and lateral pu t of the parietal bone, from all the pars 
(quamofa of the temporal bone, from the external angu¬ 
lar procefs of tire os frontis, from the temporal procefsof 
the fphenoid bone, and from an aponeurofis which co¬ 
rners it; from thefe different origins the fibres defeend 
like radii towards the jugum, under which they pafs; and 
are inferted into the upper part of the coronoid procefs of 
the lower jaw. This mufcle is covered by a tendinous 
membrane, called its aponeurofis , which arifes. from the 
bones that give origin to the tipper and femicircular part 
ol the mufcle; and, defeending over it, is inferted into all 
the jugum, and the adjoining part of the os frontis. The 
rife of this membrane is to give room for the origin of a 
greater number of flefhy fibres, to fortify the mufcle in 
its aCtion, and to ferve as a defence to it. 2. MaJJeter , ari¬ 
fes from the fuperior maxillary bone, where it joins the 
os make; and is inferted into the angle,of the lower jaw, 
ferving to pull the lower to the upper jaw, and a little for¬ 
wards and backwards. 3. Pterygoideus interims , arifes from 
tite inner and upper part of tire internal plate of the pte¬ 
rygoid procefs, filling all the fpace between the two plates. 
It is inferted into the angle of the lower jaw internally ; 
and ferves to draw' the jaw upwards, and obliquely to¬ 
wards the oppofite fide. 4. Pterygoideus externus, arifes 
from the outer fide of the external plate of the pterygoid 
procefs of the fphenoid bone, from part of the tuberofity 
of the os maxiliare adjoining to it, and from the root of 
the temporal procefs of the fphenoid bone. It is inferted 
into a cavity in the neck of the condyloid procefs of the 
lower jaw; which it pulls forwards, and to the oppofite fide. 
Muscles about the antertor tart of the Neck.— 
On the fide of the neck are two ntufcles or layers. 1. Muf- 
culus cutancus, vulgo platyfma. myoides, arifes from the cellu¬ 
lar fubftance that covers the upper parts of the deltoid 
and pedforal mufcles; in their afeent, they all unite to form 
a thin mufcle, w hich runs obliquely upwards along the 
fide oi the neck, adhering to the (kin; and are inferted 
into the lower jaw, between its angle and the origin of 
the deprelfor anguli oris, to which it is firmly connected. 
It afilfts the depreflor anguli oris in drawing the (kin of 
the cheek downwards; and; when the mouth is (hut, it 
draws all that part of the fkin, to which it is connedled, 
below the lower jaw, upwards. 2. Sterno-cleido-mafoidcus , 
arifes by two diftirnft origins ; the anterior, from the top 
cf the fternum; the pofterior, from the upper and anterior 
part of the clavicle ; both unite a little above the anterior 
articulation of the clavicle, to form one mufcle, which 
runs obliquely upwards and outwards, to be inferted, by 
a thick ftrong tendon, into the maftoid procefs, which it 
furrounds ; and, gradually turning thinner, is inferted as 
far back as the lambdoid future. It turns the head to one 
fide, and bends it forwards. 
Musci.es between the Lower Jaw and Os Hyoides. 
—There are four layers before, and two mufcles at the 
fide. The four layers are, 1. Digaffricus, arifes from the 
foffa at the root of the maftoid procefs of the temporal 
bone, and runs downwards and forwards ; then it is fixed 
by a ligament to the os hyoides; and, having received 
from that bone an addition of tendinous and mufcular fi¬ 
bres, runs obliquely forwards, and is inferted into a rough 
(inuofity at the inferior and anterior edge of the chin. Its 
ufe is to open the mouth; and, when the jaws are (hut, to 
raife the larynx and pharynx upwards, as in deglutition. 
2. Mylo-hyoideus, arifes from the infide of the lower jaw, 
between the laft dens molaris and the middle of the chin, 
where it joins with its fellow. It is inferted into the lower 
edge ot the bafis of the os hyoides, and ferves to pull the os 
hyoides forwards, upwards, and to a fide. 3. Genio-hyoi- 
deus, arifes from a rough protuberance in.the middle of the 
lower jaw internally ; is inferted into the bafis of the os 
hyoides; and draws this bone forwards to the chin. 4. 
Genio-hyo-glojfus, arifes from the middle of the lower jaw ; 
its fibres run, like a fan; and are inferted into the tongue, 
Vox,. I. No. 36. 
and bafe of the os hyoides, near its cornu. It ferves to 
draw the tip of the tongue backwards into the mouth, the 
middle downwards, and to render itsdorfutn concave; to 
draw its root and os hyoides forwards, and to thruft the 
tongue out of the mouth. 
The two mufcles at the fide are, 1. Uyo-glcfus , arifes 
from the bafe, cornu, and appendix of the os hyoides; the 
fibres run upwards and outwards, to be inferted into the 
fide of tlie tongue, near the ftylo-glogus ; and pulls the 
tongue inwards and downwards. 2. Lingualis, arifes from 
the root of the tongue laterally; runs forwards between 
the hyo-gloffiis and genio-gloflus, to be inferted into the 
tip of the tongue, along with part of the ltylo-gloffus. It 
ferves to contraCt the fubftance of the tongue, and bring 
it backwards. 
Muscles between the Os Hyoides and Trunk.— 
Thefe may be divided into two layers. The firft layer con- 
(ifts of two mufcles. 1 . Sterne-hyoidtus, arifes from the 
cartilaginous extremity of the firft rib, the upper and in¬ 
ner part of the fternum, and from the clavicle where it 
joins with the fternum. It is inferted into the bafe of the 
os hyoides; and its ufe is to pull the os hyoides down¬ 
wards. 2. Omo-hyoideus, arifes from the fuperior coffa of 
the fcapula, near the femilunar nitch, and from tiie liga¬ 
ment that runs acrofs it; thence, afeending obliquely, is 
inferted into the bafe of the os hyoides, between its cornu 
and the infertion of the fterno-hyoides. Its ufe is to pull 
the os hyoides obliquely downwards. 
The fecond layer confifts of three mufcles. 1. Stcrno - 
thyroideus, arifes from the whole edge of the uppermoft 
bone of the fternum internally, oppofite to the cartilage of 
the firft rib, from which it receives a fmall part of its ori¬ 
gin. It is inferted into the furface of the rough line at 
the external part of the inferior edge of the thyroid car¬ 
tilage, and is ufed to draw the larynx downwards. 2. 
T/iyreo-hyoideus, arifes froili the rough line, oppofite to the 
former ; is inferted into part of the bafes, and almoft ail 
the cornu of the os hyoides; and its ufe is to pull the os 
hyoides downwards, or the thyroid cartilage upwards. 3. 
Crico-thyroidcus, arifes from the fide and fore-part of the 
cricoid cartilage, and is inferted by two portions; the firft, 
into the lower part of the thyroid cartilage; the fecond, 
into its inferior cornu. It pulls forwards and depreffes the 
thyroid, and elevates and draws back tliecricoid, cartilage. 
Muscles between the Lower Jaw and Os Hyoides 
laterally.—Thefe are five-in number. Thefe proceed from 
the ftyloid procefs of the temporal bone, from which they 
have half of their names; and two from the pterygoid procefs 
of the fphenoid bone. The three from the ftyloid procefs 
are, 1. Stylo-glojfas , arifes from the ftyloid procefs, and from 
a ligament that connects that procefs to the angle of the 
lower jaw. It is inferted into the root of the tongue, runs 
along its fide, and is infenfibly loft near its tip. It ferves 
to draw the tongue laterally and backwards. 2. Stylo-hyoi- 
deus, arifes from the middle and inferior part of the ftyloid 
procefs; is inferted into the os hyoides at the junction of 
the bafe find cornu; and ferves to pull the os hyoides to 
one fide, and a little upwards. Its flefhy belly is gene¬ 
rally perforated by the tendon of the digaftric mufcle, on 
one or both fides. There is often another accompanying 
it, called fylo-hyoideus alter .; and has the fame origin, in¬ 
fertion, and ufe. 3. Stylo-pharyngeui, arifes from the root 
of the ftyloid procefs; is inferted into the (ide of the pha¬ 
rynx and back-part of the thyroid cartilage, and ferves to 
dilate and raife the pharynx and thyroid cartilage upwards. 
The two from the pterygoid procefs are, 1. Circumfexits, 
or tehforpalati, arifes from the fpinous procefsof the fphe¬ 
noid bone, behind the foramen ovale ; it then runs down 
the pterygoideus interims, pafles over the hook of the in¬ 
ternal plate of the pterygoid procefs, and is inferted in f o 
the velum pendulum palati, and the femilunar edge of the 
os palati, and extends as far as the future which joins the 
-two bones. Its ufe is to ftretch the velum, to draw it 
downwards, and to a fide towards the ’took. It has little 
effect upon the tube, being chiefly connect ed .to its ofl'eous 
.7 F part,. 
