Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29465/948/
938 TEMPORO-MAXILLARY ARTICULATION. 
The internal lateral ligament is a long thin 
slip extending from the spinous process of the 
sphenoid, and the neighbouring parts of the 
temporal bone to the fore part of the lip of 
the inferior dental canal. It lies behind the 
external pterygoid muscle, by the origin of 
which its cranial attachment is concealed, and 
it is separated from the temporo-maxillary joint 
by a considerable space through which pass 
the internal maxillary artery and vein, giving 
off their middle meningeal and inferior dental 
branches, which indeed are conducted, the 
former to the foramen spinosum of the sphe¬ 
noid, the latter to the inferior dental canal, by 
the ligament in question. 
Numerous stray fibres of ligamentous tissue 
strengthen the synovial sacs of the temporo- 
maxillary joint, forming a kind of capsular 
ligament. 
That process of the cervical fascia, which 
is called the stylo-maxillary ligament, is gene¬ 
rally enumerated as one of the ligaments of 
this joint. It extends from the styloid process 
to the lower part of the ramus of the jaw, 
separating the parotid from the submaxillary 
gland, and affording attachment to the stylo¬ 
glossus muscle. The condyle of the lower 
jaw depends for the maintenance of its normal 
apposition to the temporal bone much more 
upon the masseter, temporal and pterygoid 
muscles than upon these small ligaments ; by 
these, however, its astero-posterior gliding is 
indifferently tethered. 
Muscles. — The external pterygoid-muscle, 
proceeding backwards and outwards from its 
origin, is mainly inserted into the front of the 
neck that supports the maxillary condyle, the 
upper part of it, however, is inserted into the 
interarticular fibro-cartilage, which thereby is 
drawn forward along with the condyle when 
this muscle acts. This insertion is tendinous. 
Motions of the joint. — The temporo-maxil¬ 
lary joint admits of a ginglymoid motion in the 
vertical direction, by which the mouth is 
opened and shut. This motion must of ne¬ 
cessity always take place in the joints of both 
sides at the same instant. It also admits of a 
horizontal antero-posterior gliding motion, in 
which the joint of one side only may be mainly 
concerned. In the human subject the front 
teeth of the lower jaw, in most cases, are not ex¬ 
actly opposed to those of the upper jaw—that 
is, the summits of the one set are not applied 
to the summits of the other — in the ordinary 
position of the mouth, either when at rest or 
engaged in mastication. The lower incisor 
teeth are usually posterior to the upper. But 
when we bite with the front teeth we bring 
the upper and lower set into apposition by 
thrusting forward the lower jaw : in this act 
both joints are similarly concerned. We can 
also execute a grinding motion from side to 
side, and this is done by thrusting forward one 
condyle whilst the other merely revolves on 
the axis of its neck. 
The jaw is elevated or closed by the tem¬ 
poral, masseter, and pterygoid muscles. The 
pterygoid, chiefly the external, are the agents 
in protruding it. These latter are antagonised 
by the elevating and also by the depressing 
muscles. The chief depressor of the lower 
jaw is the digastric, as is clearly shown by its 
comparative anatomy, but all those which ex¬ 
tend from the chin to the hyoid bone are 
capable of, and occasionally do assist in per¬ 
forming this act. 
The majority of the muscular fibres that 
elevate the jaw arrive at their insertion into 
it from before backwards ; thus the masseter 
has a kind of twist in the arrangement of 
its fibres, so that those which arise most 
anteriorly are inserted very conspicuously 
furthest back, whilst the remainder proceed 
directly downwards or slightly forwards ; a 
considerable portion of those of the temporal, 
namely, those which arise from the anterior 
part of the temporal fossa, run backwards to 
their insertion into the coronoid process. 
The use of this arrangement seems, upon a 
careful consideration of the mechanics of the 
question, to be the application of the elevating 
or closing force in a more favourable direc¬ 
tion, not, as might seem at first sight, the 
protrusion of the lower jaw — that is amply 
effected by the pterygoideus externus. 
Abnormal conditions of the temporo- 
maxillary joint.—Accidents.— The condyle 
of the lower jaw can only be dislocated in one 
direction, namely forwards. In this accident 
the condyle slips forward over the inferior root 
of the zygoma, and is then drawn somewhat 
upwards within the zygomatic arch. The inter¬ 
articular cartilage is carried with it. Thisusually 
happens to the joints of both sides, but occa¬ 
sionally one condyle only is dislocated. It is 
usually produced by the action of the muscles 
when the mouth is very widely opened, as in 
yawning, or more especially in biting a very 
large object, such as a large apple. 
When both the condyles are dislocated, the 
lower jaw is thrust forwards and cannot be re¬ 
tracted. The mouth is widely open and the 
patient is unable to close it. The power of 
swallowing is lost, and the saliva, the secretion 
of which is probably increased, flows from the 
mouth involuntarily. Articulation is difficult, 
owing to the impossibility of making the labial 
sounds. There is a conspicuous depression 
beneath the zygoma just in front of the ear, 
and a flatness in the masseteric region. The 
coronoid process is much depressed, and forms 
a visible protuberance beneath the zygoma, 
and, as first observed by Mr. Adams of Dub¬ 
lin, there is a prominence in the temporal re¬ 
gion between the eyebrow and the ear, pro¬ 
duced by the posterior fibres of the temporal 
muscle being pushed up by the condyle in its 
new position. 
If this dislocation remains unreduced, the 
parts, as in most other dislocations, gradually 
accommodate themselves to their new position, 
so that the power of articulation and deglu¬ 
tition is re-acquired, the mouth can be closed, 
and a considerable amount of motion is re¬ 
gained, but the chin remains abnormally thrust 
forwards, and there is always a depression in 
the position normally occupied by the con¬ 
dyle.
        

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