176 . HEAD AND NECK 



it and the neck of the mandible ; whilst, still lower, the 

 inferior alveolar vessels and nerve are interposed between 

 it and the ramus of the mandible. 



The stylo-mandibular ligament is a fibrous band, derived 

 from that portion of the deep cervical fascia which forms 

 a part of the capsule of the parotid gland. It is attached, 

 above, to the styloid process, and, below, to the angle and 

 posterior border of the ramus of the mandible, between the 

 internal pterygoid and masseter muscles. 



An examination of the spheno-mandibular and stylo- 

 mandibular ligaments will show that very little is added to 



the strength of the joint by 

 their presence. The security 

 of the joint depends not so 

 much upon its ligaments as 

 upon the strong muscles of 

 mastication, which keep the 

 head of the mandible in its 

 place. 



The articular disc is an 

 / oval plate of fibre-cartilage, 

 ' with its long axis directed 

 transversely. It is inter- 

 '' posed between the condyle 



FIG. 65. Diagram of the different o f t h e mandible below and 



positions occupied by the head of the ,, j-u i r <r\ T 1 



mandible and the discus articularis the mandlbular fossa (O.T. 

 as the mouth is opened and closed. glenoid) and the articular 



tubercle (O.T. eminentia 



articularis) above, and it divides the joint cavity into an upper 

 and a lower part, each of which is provided with a separate 

 synovial lining. To expose the disc, the temporo-man- 

 dibular ligament must be removed. The disc will then be 

 seen to be adapted to the two bony surfaces between which 

 it lies. Above, it is concavo-convex in correspondence with 

 the tuberculum articulare and the mandibular fossa of the 

 temporal bone ; whilst below, it is concave, and fits upon 

 the upper aspect of the condyle of the mandible. In the 

 centre it is thin, and in some cases it is perforated. Its 

 circumference is thick, more especially posteriorly. It should 

 be noted also that the external pterygoid muscle is partly 

 inserted into the capsule at its anterior border. 



The synovial stratum which lines the capsule enclosing the 



