338 



THE MUSCULATURE 



Relations. — The superficial ascending branch of the auriculo-temporal nerve usually runs 

 superficial to the anterior and superior auricular muscles. The superficial temporal vessels run 

 at first beneath these muscles and the lateral expansion of the galea aponeurotica, then between 

 the two fascial layers which enclose the muscles. Their branches of distribution finally come 

 to lie between the muscles and aponeurosis and the skin. The posterior auricular artery and 

 nerve usually run under cover of the auricularis posterior. 



Action. — The anterior muscle is a protractor, the superior an elevator, and the posterior a 

 retractor of the ear, but usually in man they are inactive. 



Variations. — These muscles vary much in development. The most constant of them is 

 the superior. The posterior frequentlj^ is increased in size and may be fused with the occipitalis, 

 which originally was probably an ear muscle. From the anterior muscle a special deep fasciculus 

 is occasionally isolated. Each of the muscles is occasionally, though rarely, absent, the anterior 

 most frequently. An inferior auricular muscle is very rarely found in man, though present in 

 many of the lower mammals. A slip of the posterior auricular may run beneath the ear to the 

 parotid fascia. 



Fig. 345. — The Temporal Muscle. 



Temporal 



Buccinator" 



2. CRANIO-MANDIBULAR MUSCULATURE 

 (Figs. 344, 345, 346, and 347) 



The cranio-mandibular muscles, or muscles of mastication, pass from the base 

 of the skull to the lower jaw. They are represented in the selachians by a single 

 muscle mass, the adductor mandibulse (Gegenbaur), but in the higher vertebrates 

 this muscle mass becomes variously subdivided during embryonic development. 

 The muscles are innervated by the masticator nerve (motor root of the tri- 

 geminal cranial nerve, the nerve of the mandibular arch). In man four muscles 

 are recognised, the temporal, masseter, and internal and external pterygoids. 



The temporal and masseter muscles are situated on the lateral surface of the 

 skull, partly under cover of muscles of the facialis group. The temporal muscle 

 (fig. 345), which resembles the quadrant of a circle, arises from the temporal 

 fossa and is inserted into the coronoid process of the mandible; the thick, quad- 

 rilateral masseter (fig. 344) musc^le arises from the zygomatic arch and is in- 

 serted into the lateral surface of the ramus and angle of the mandible. The 

 pterygoids (fig. 340) are more deeply seated. The cone-shaped external pterygoid 

 arises from the lateral side of the pterygoid process and lower surface of the great 

 wing of the sphenoid and is inserted into the condyloid process of the mandible 

 and the capsule of the joint. The thick, quadrilateral internal pjteiygjaid parallels 

 the masseter. It arises from the pteiygoid fossa of the sphenoid and is inserted 

 into the inner side of the angle of the mandible. It will be noted that the tem- 



