6 4 



APPLIED ANATOMY. 



foramen on or near its upper surface; therefore, in operating for neuralgia in the 

 aged, if it is desired to attack the mandibular nerve in its canal, it should be searched 

 for nyar the upper border of the bone. 



In infancy the teeth, not having erupted, are contained in the jaw, the alveolar 

 portion is, therefore, large. The basal portion, on the contrary, is quite small, serv- 

 ing merely as a narrow shelf on which the unerupted teeth lie. As the mandibular 

 nerve runs beneath the teeth, the mental foramen is of necessity comparatively low. 

 At birth the condyle is about level with the upper portion of the symphysis, and the 

 body forms with the ramus an angle of 175 degrees. At the end of the fourth year 

 the angle has decreased to about 1 40 degrees. By adult age the angle has decreased 

 to about 115 degrees, and as the teeth are lost the angle gradually increases until it 

 again reaches 140 degrees. 



Temporomandibular Articulation. A knowledge of the movements of the 

 jaw is essential to a proper understanding of the fractures and dislocations to which 

 it is subject. 



Temporalis 



Discus articularis 



_ Processus condyloideus 



Pterygoideus externus 



FIG. 72. The temporomandibular articulation. 



The mandible articulates with the glenoid fossa and its anterior edge or emi- 

 nentia articularis of the temporal bone. Interposed between the condyle below and 

 the bone above, is an interarticular cartilage. This divides the articulation into 



two portions, an upper and a lower. The ligaments 

 are a capsular, strengthened by an external lateral 

 (temporomandibular) and an internal lateral. The 

 capsular ligament is weakest anteriorly and strongest 

 on the outer side. The thickening of the capsule 

 on its outer side forms the external lateral or tem- 

 poromandibular ligament. The sphenomandibular 

 or internal lateral ligament is practically distinct 

 from the articulation. It runs from the alar spine 

 on the sphenoid above to the mandibular spine or 

 lingula, just posterior to the mandibular foramen 

 below. Between it and the neck of the bone run 

 the internal maxillary artery and vein. When the 

 condyle glides forward it puts the posterior portion 



of the capsule on the stretch, and if the jaw is dislocated this part of the capsule is 

 torn. The interarticular cartilage is more intimately connected with the lower por- 

 tion of the articulation. The same muscle that inserts into the neck of the jaw (the 

 external pterygoid) likewise inserts into the cartilage ; therefore, the two move 

 together, so that when the condyle goes forward the cartilage goes forward and rides 

 on the eminentia articularis. 



FIG. 73. External lateral ligament of the 

 lower jaw. 



