FACE AND FRONTAL REGION OF HEAD 13 



It helps to depress the mandible and is supplied by the 

 facial nerve. 



Dissection. Cut through the posterior half of the platysma 

 along the lower border of the mandible ; detach the risorius 

 from the fascia on the masseter ; then turn the risorius and the 

 detached part of the platysma towards the angle of the mouth. 

 Whilst doing that be careful to avoid injuring the branches of 

 the vessels and nerves of the face (Figs. 4, 5, 15). 



As soon as the platysma and the risorius are reflected search 

 below the level of the ear for branches of the great auricular 



- M. quaclratus labii superioris, 

 caput angulare 



M. quadratus labii 

 superioris, caput 

 infraorbitale 



M. caninus 



M. triangularis 



M. quadratus labii inferioris 



FIG. 3. Diagram of the Orbicularis Oris Muscle. 

 The fibres which enter it from the buccinator are not represented. 



nerve which ascend over the lower part of the parotid gland, 

 Some of them pierce the parotid and terminate in its substance, 

 others end in the skin of the masseteric region. 



Find the anterior facial vein and the external maxillary artery 

 at the lower and anterior angle of the masseter, as they cross 

 the lower border of the mandible. Clean them at that point, 

 but do not trace them towards their terminations at present. 



At the posterior border of the mandible note the deep fascia 

 over the superficial surface of the parotid gland; it is called 

 the parotid fascia. It ascends from the fascia of the neck, 

 and is attached above to the zygomatic arch. Note also that 

 at the anterior border of the parotid the parotid fascia blends 

 with the fascia on the superficial surface of the masseter 

 muscle. Cut through the fascia covering the parotid gland 

 immediately anterior to the ear, extending the incision from 

 the zygoma above to the angle of the mandible below ; then 



