THE SUPERFICIAL CERVICAL MUSCLE 387 



inserted into a depression in front of the neck of the condyle of the mandible, and 

 into the front margin of the articular disk of the temporomandibular articulation. 

 The Pterygoideus interims (Internal pterygoid muscle) (Fig. 383) is a thick, quad- 

 rilateral muscle. It arises from the medial surface of the lateral pterygoid plate 

 and the grooved surface of the pyramidal process of the palatine bone; it has a 

 second slip of origin from the lateral surfaces of the pyramidal process of the pala- 

 tine and tuberosity of the maxilla. Its fibers pass downward, lateralward, and 

 backward, and are inserted, by a strong tendinous lamina, into the lower and back 

 part of the medial surface of the ramus and angle of the mandible, as high as the 

 mandibular foramen. 



FIG. 383. The Pterygoidei; the zygomatic arch and a portion of the ramus of the mandible have been removed. 



Nerves. The muscles of mastication are supplied by the mandibular nerve. 



Actions. The Temporalis, Masseter, and Pterygoideus internus raise the mandible against 

 the maxillse with great force. The Pterygoideus externus assists in opening the mouth, but its 

 main action is to draw forward the condyle and articular disk so that the mandible is protruded 

 and the inferior incisors projected in front of the upper; in this action it is assisted by the Ptery- 

 goideus internus. The mandible is retracted by the posterior fibers of the Temporalis. If the 

 Pterygoidei internus and externus of one side act, the corresponding side of the mandible is 

 drawn forward while the opposite condyle remains comparatively fixed, and side-to-side move- 

 ments, such as occur during the trituration of food, take place. 



THE FASCIA AND MUSCLES OF THE ANTERO-LATERAL REGION 



OF THE NECK. 



The antero-lateral muscles of the neck may be arranged into the following 

 groups : 



I. Superficial Cervical. III. Supra- and Infrahyoid. 



II. Lateral Cervical. IV. Anterior Vertebral. 



V. Lateral Vertebral. 



I. THE SUPERFICIAL CERVICAL MUSCLE. 



Platysma. 



The Superficial Fascia of the neck is a thin lami'na investing the Platysma, 

 and is hardly demonstrable as a separate membrane. 



