FACE AND FRONTAL REGION OF HEAD 7 



maxillary bone, and trace it downwards to the orbicularis oris, 

 but avoid injury to the angular vein which lies on its super- 

 ficial surface. Medial to the angular head of the quadratus 

 labii superioris find and clean the pars transversa of the musculus 

 nasalis, which lies across the lower part of the bridge of the 

 nose. Below the pars transversa it may be possible to dis- 

 play the pars alaris which passes from the maxilla tJ5 the ala of 

 the nose. 



Now turn to the lower border of the mandible and clean the 

 platysma, a broad thin sheet of muscle which ascends from the 

 neck. Its anterior fibres are inserted into the anterior part of 

 the lower border of the mandible. The posterior fibres ascend 

 across the mandible, then they turn forwards to the angle of 

 the mouth, as the risoritis. Above and in front of the risorius 

 find the zygomaticus, a slender muscle which descends from 

 the zygomatic bone to the angle of the mouth, where it blends 

 with the orbicularis oris. Now follow the angular vein down- 

 wards and backwards. At the lower margin of the orbit it 

 becomes the anterior facial vein ; follow that vein downwards 

 and backwards to the point where it disappears under cover of 

 the zygomaticus. Below and in front of the anterior facial 

 vein the terminal part of the external maxillary artery may be 

 found on the superficial surface of the quadratus labii superioris, 

 but it may lie deep to that muscle. After the anterior facial 

 vein has been cleaned, in the area indicated, raise the lower 

 fibres of the orbicularis oculi and reflect them towards the 

 palpebral fissure ; then clean the infra - orbital head of the 

 quadratus labii superioris, a flat and fairly wide muscle which 

 springs from the lower margin of the orbit, under cover of 

 the orbicularis oculi, and descends to the upper lip, where 

 it blends with the orbicularis oris. Lateral to the infra- 

 orbital head, the small zygomatic head of the quadratus labii 

 superioris may be found. It descends from the zygomatic 

 bone and blends with the lower part of the lateral border of 

 the infra-orbital head. After the zygomatic head has been 

 cleaned turn to the lower lip region and clean the triangu- 

 laris. It springs from the mandible above the insertion of the 

 anterior part of the platysma and passes upwards to the angle 

 of the mouth, where it blends with the orbicularis oris. Anterior 

 to the triangularis, and on a deeper plane, find and clean the 

 quadralus labii inferioris. It springs from the mandible under 

 cover of and anterior to the triangularis and ascends to the 

 orbicularis oris, with which it blends. After the muscles 

 mentioned have been defined proceed to the detailed study of 

 their positions and attachments. 



Orbicularis Oculi. The orbicular muscle of the eyelids, 

 on each side, consists of a thick orbital portion which covers 

 the superficial bony boundaries of the orbit, and a thinner 

 and paler palpebral part which lies in the eyelids. 



The orbital portion of the muscle extends upwards to the 

 forehead, laterally to the temporal region and downwards into 

 the cheek. Its fibres are relatively dark and coarse. They 

 all take origin medially from the medial part of the palpebral 



