MUSCLES OF MOUTH. 39 



with the rest of the muscles, but the greater number are continued into 

 the depressor anguli oris and the lower lip. 



Action. This muscle elevates the corner of the mouth, and acts as an 

 antagonist to the depressor. 



The DEPRESSOR ANGULI ORIS (fig. 6, ls ) is triangular in shape ; it 

 arises from the oblique line on the outer surface of the lower jaw, and 

 ascending to the angle of the moutlv, its fibres are prolonged into the ele- 

 vator of the angle. The muscle conceals the labial branch of the inferior 

 dental vessels and nerve. At its origin the depressor is united with the 

 platysma myoides, and near its insertion with the risorius muscle. 



Action. The angle of the mouth is drawn downwards and backwards 

 by it, as is exemplified in a sorrowful countenance. 



The ZYGOMATIC MUSCLES (fig. 6) are directed obliquely from the arch 

 of the same name towards the angle of the mouth and the upper lip. 

 One is longer and larger than the other ; they are therefore named major 

 and minor. 



The zygomaticus major, 8 , arises from the outer part of the malar bone, 

 and is inserted into the angle of the mouth. 



The zygomaticus minor, ', is attached to the malar bone anterior to the 

 other, and blends with the fibres of the special elevator of the upper lip. 



Action. The large muscle inclines upwards and backwards the corner 

 of the mouth ; and the small one assists the levator labii superioris in 

 raising the upper lip. 



The KISORIUS MUSCLE (Santorini) (fig. 6, 9 ) is a thin and narrow bun- 

 dle of fibres, sometimes divided into two or more parts, which arises 

 externally from the fascia over the masseter muscle, and is connected in- 

 ternally with the apex of the depressor anguli oris. 



Action. The use of this muscle is indicated by its name, as it retracts 

 the corner of the mouth in laughing. 



The BUCCINATOR (fig. 6, u ) is the flat and thin muscle of the cheek, 

 and occupies the interval between the jaws. The muscle arises from the 

 outer surface of the alveolar borders of the upper and lower maxillae, as 

 far forwards in each as the first molar tooth ; and in the interval between 

 the jaws behind it is attached to a band of fascia the pterygo-maxillary 

 ligament. From the origin the fibres are directed forwards to the angle 

 of the mouth, where they mix with the other muscles and with both parts 

 of the orbicularis ; and as some of the central fibres descend to the lower 

 lip whilst others ascend to the upper lip, a decussation takes place at the 

 corner of the mouth. 



On the cutaneous surface of the buccinator are the different muscles 

 converging to the angle of the mouth ; and crossing the upper part is 

 the duct of the parotid gland, which perforates the muscle opposite the 

 second upper molar teeth. Internally the muscle is lined by the mucous 

 membrane of the mouth, and externally it is covered by a fascia (bucco- 

 pharyngeal) that is continued to the pharynx. By its intermaxillary 

 origin the buccinator corresponds with the attachment of the superior 

 constrictor of the pharynx. 



Action. By one muscle the corner of the mouth is retracted, and the 

 cheek wrinkled. By the action of both the aperture of the mouth is 

 widened transversely. 



In mastication the cheek is pressed by the muscular contraction against 

 the dental arches, when the corner of the mouth is fixed by the sphincter. 



In the expulsion of air from the mouth, as in whistling, the muscle is 



