938 



TEMPORO-MAXILLAUY 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 pte r ygoid 

 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 ofthejdnt. 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 a'ways 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 

 tee;th 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 

 condyie 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 \\hich 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 ptcrygoideus 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. 



