THE TEMPORO-MAXILLARY ARTICULATION. 163 



wards and a little forwards, to be attached to the lingula and the lower border of 

 the inferior dental foramen. Between it and the lower jaw are placed the external 

 pterygoid muscle, the internal maxillary vessels, the auriculo-temporal nerve, and 

 the inferior dental vessels and nerve. 



The internal lateral ligament is formed in the tissue surrounding a part of Meckel's 

 cartilage (p. 78). 



The interarticular disc or meniscus is a thin plate of fibro-cartilagc 

 placed between the articular surfaces of the bones. It is of an oval form, broadest 

 transversely, thickest posteriorly, and thinnest at its centre, where It is sometimes 

 perforated. The inferior surface, which is in contact with the condyle, is concave ; 

 the superior is concavo-convex from before backwards, conforming with the articular 

 surface of the temporal bone. Its circumference is attached closely to the capsule, 

 and anteriorly a part of the external pterygoid muscle is inserted into it. 



Synovial sacs. The synovial sac between the interarticular disc and the 

 glenoid cavity is larger and looser than that which is interposed between the disc 



Fiji. 191. SAGITTAL SECTION OP THE TEMPORO- 

 MAXILLARY ARTICULATION OP THE RIGHT 

 SIDE. (Allen Thomson.) ^ 



1, is placed close to the articular eminence, 

 and points to the superior synovial cavity of the 

 joint ; 2, is placed close to the articular surface 

 of the condyle of the lower jaw, and points to 

 the inferior synovial cavity of the joint ; x , is 

 placed on the thicker posterior portion of the 

 interarticular disc. 



and the condyle of the jaw. "When 

 the fibro-cartilage is perforated, the 

 upper and lower synovial cavities neces- 

 sarily communicate with each other. 



The stylo-maxillary ligament is 

 the name given to a strong band of 

 the cervical fascia extending from the styloid process to the" angle and posterior 

 border of the ramus of the jaw, where it is inserted between the masseter 

 and internal pterygoid muscles. It separates the parotid from the submaxillary 

 gland. 



It may be proper also to mention here the stylo-hyoid ligament, a thin 

 fibrous cord, which passes from the point of the styloid process to the lesser cornu 

 of the hyoid bone, and suspends that bone from the styloid process. A consider- 

 able portion of the stylo-hyoid ligament is sometimes converted into bone in the 

 human subject, and in many animals it is naturally osseous, constituting the epihyal 

 bone. 



Movements. The jaw is capable of movements of elevation and depression, and of 

 protrusion and retraction ; but it is to be observed that when the jaw is depressed, as in 

 opening the mouth, the condyle advances from the glenoid cavity so as to be placed on the 

 articular eminence in front of it. The movements which take place in the superior and 

 inferior compartments of the joint are of different kinds. In the upper the fibro-cartilage 

 glides forwards and backwards on the temporal bone ; in the lower compartment the 

 condyle rotates on a transverse axis against the fibro-cartilage. In opening the mouth the 

 two movements are combined ; the jaw and fibro-cartilage together move forwards and rest 

 on the convex root of the zygoma, while at the same time the condyle revolves on the fibro- 

 cartilage. The point of least movement corresponds approximately to the position of the 

 inferior dental foramen, so that stretching of the inferior dental nerve is avoided. When the 

 lower incisors are protruded beyond those of the upper jaw, the movement is confined chiefly 



VOL. II. M 



