DEGLUTITION. 
mouth is opened; but the motion is common to the whole 
of the cranium w ith t jaw. The back of the head de- 
3 and the eee 
p- 10.) ; butt 
takes pla ce in ordinary ei 
pene himfelf thus: ‘* motum, qu 8 aperitur, pce 
inferiori non motd, {ed capite retrorfum duéto, per biv 
trem.” Any individual ay fatisfy himfelf, that bis foe 
jaw does afcend, when the mouth is opened, if he will ftand 
oppofite to a looking: glafs, holding the point of a knife juft 
againit the lower edge of the upper teeth, and then open his 
3 
‘ 
outh. 
rae fia of the lower Faw.—This may be depreffed, 
elevated, mo backwards, forwards, and to either fide. 
the glenoid walk ie that the upper part becomes rather 
anterior; the a the bone move backwards, and the 
a procat ead. When the depreffion is flight, 
n r effe& is produced; but if a more confiderable 
- the mouth be needed, the ok is carried 
the tem- 
n ed ody. 
forwards with the condyle; the rotation of whic 
at the fame time, its pofterior portion is brought into cons 
taéi with the articular eminence. The angle is carried se 
ther and farther backwards, fo that it moves juft in ano 
pofite dire€tion to the condyle; the external ligament is 
rather tenfe, as well as the pofterior part of the u upper fy- 
novial membrane; and the ilylo-maxillary ligament is re- 
ver 
Jaxed. If the dep 
da 
may become piped, by flipping in front of 
the pee emin 
The elevation of hes aw is effected by a motion of the 
bone in an inverfe dire€tion to that whi ch has been juft de- 
{cribed. 
arrived in that art, it ftill continues to turn u 
til the motion is arr see y th r teeth meetin 
If the depreffion has ie i acento the 
erl 
up em whic is ciel ly 
ery ioale a folded on self i in ie cellulsy {pace be- 
tad the fiffura Glaferi. 
The jaw is mond forwards without any thing like that 
seven. which we have defcribed i in the depreflion. ‘The 
whole bone is moved horizontally ; and all the ligaments 
become equally tenfe, The fuperior fynovial membrane is 
ftretched at its back part; while the inferior remains in its 
natural ftate, fince it accompanies the condyle in its motion 
forwards. For the pterygoideus externus, by which that 
motion is performed, attaching itfelf to both parts, carries 
them forwards together. This common infertion is effentia 
for the purpofe of preferving the condyle and cartilage in- 
ae proper relative pofitions. If the motion forwards were 
d to a great extent, the coronoid procefs would 
ie againft the anterior aa of the temporal foffa, and 
prevent any luxation; for which it is receflary that that 
fhouid be seprelfed 
t as the cartilage ale up much of the glenoid cavity, this 
bacon is very lig 
In the motion ee the whole jaw moves horizon- 
tally through the fame fpace in which it had paffed a 
ds; and by a movement precifely aie inverfe of tha 
which we have juft defcribed. 
The lateral motion of the jaw is not of an horizontal na- 
ture. 
t 
nalis are the obftacles 
inwards or outwards is mani ev aenyt . Tf the chin 
It quits the geno ca 
wards under the articular eminence, and 
ated feparately, if the effort oe a confiderable. 
ftate of the left joint is then nearly the fame as in the de- 
preffed condition of the jaw. The reader will of courfe un- 
derftand that the chin is carried towards the left by a 
cular bony ridge, which, beginning juft behind the orbit, 
paffes backwards in an arched courfe over the middle of the 
parietal bone, and then turns abies and downwards, fo as 
to become continuous with the bony ridge which feparates 
the fq rtions of the temporal bone. 
(For a particular defcription of this ridge, and of the fpace 
included wi P lu d denfe 
aponeurofis arifes from the whole extent of the temporal 
ridge, and, covering the mufcle, is implanted firmly in the 
fuperior edge of the zygoma, and in the outer edge of the 
orbit. By means of this, a complete cavity is prepared for 
holding the mufcle ; having its inner furface formed of the 
cranium, and the outer furtace of this temporal fafcia; and 
opering below by rae ae left between the zygoma an 
the furface of the The mu(cle arifes then in a fle 
o os frontis, temporis, {phenoides, — 
adly, from the inner furface of the zygoma; 
from the whole inner furface of the ase fen 
thefe parts two layers of ficfhy fibres are produced, 
ternal and external; and thefe are implanted in a middle 
5 radiate 
