176 MUSCLES OF THE HEAD AND NECK. 



surface supports the infraorbital nerve and artery, which separate it from the preceding 

 muscle; the posterior surface lies on the superior maxilla and the orbicularis and 

 buccinator muscles, with which and the depressor anguli oris the fibres are blended. 



The zygomatici are two narrow and subcutaneous fasciculi of muscular 

 fibres, extending obliquely from the most prominent part of the cheek to 

 the angle of the mouth, one being thicker and longer than the other. 



a. The zygomaticus minor, a very small muscle, arises from the anterior 

 and inferior part of the malar bone, and inclines downwards and forwards 

 to terminate by joining the outer margin of the levator labii superioris ; 

 sometimes near the origin of that muscle. It lies internal to the zygo- 

 maticus major, but distinct from it in the whole length, and is sometimes 

 joined by some fibres of the orbicularis palpebrarum : in some instances 

 it is replaced by a fleshy slip from that muscle ; in others it is altogether 

 wanting. 



b. The zygomaticus major, placed externally to the smaller muscle of the 

 same name, arises from the malar bone near the zygomatic suture, from 

 which it descends to the angle of the mouth, where it is continued into the 

 orbicularis and depressor anguli oris. 



The risorius or smiling muscle (Santorini), consisting of some very thin 

 fasciculi, commences in the fascia over the masseter, or on the parotic gland, 

 and, extending transversely inwards in the fat of the cheek, joins the orbicu- 

 laris and depressor anguli oris at the angle of the mouth. It is united with 

 the fibres of the platysma close to their termination, and is by many re- 

 garded as a part of that muscle. 



The buccinator muscle consists of a flat and thin but strong set of fibres 

 in contact with the mucous membrane, and forming a considerable part of 

 the wall of the mouth. It is attached by its upper and lower margins to 

 the outer surface of the alveolar parts of the maxillary bones, outside the 

 molar teeth, and between these bones it is fixed behind to a narrow band of 

 tendinous fibres, the pterygo-maxillary ligament, a structure which extends 

 from the internal pterygoid plate to the posterior extremity of the mylo- 

 hyoid ridge of the lower jaw close to the last molar tooth, and separates 

 the buccinator muscle from the superior constrictor of the pharynx. From 

 these points the fibres of the muscle are directed forwards, approaching 

 each other, so that the muscle is narrowed and proportionally thickened 

 near the angle of the mouth, where it becomes incorporated with the 

 orbicularis. The fibres near the middle of the muscle cross each other, 

 those from above entering into the lower lip, and those from below into the 

 upper one ; but the higher and lower fibres are directed into the correspond- 

 ing lip without decussation. 



The buccinator is covered and supported by a thin fascia, which is closely adherent 

 to the muscular fibres ; and is overlapped by the triangularis oris, the terminal fibres 

 of the platysma myoides, and by the facial artery and vein ; it is also covered by the 

 masseter and zygomatici, from which it is separated by a quantity of soft adipose 

 tissue of a peculiar character. Opposite the second molar tooth of the upper jaw, its 

 fibres give passage to the duct of the parotid gland. 



The depressor anguli oris, or triangnlaris oris, is broad at its origin from 

 a line on the external surface of the lower jaw near its base ; passing up- 

 wards it is collected into a narrower bundle which is inserted into the 

 orbicularis at the angle of the mouth. 



This muscle is covered by the skin, and, at its insertion, by the zygomaticus major, 

 under which its fibres pass ; it conceals part of the buccinator and of the depressor 

 of the lower lip. 



