34 TOPOGRAPHICAL ANATOMY OF THE 



and the ventral wall searched for a rounded, sharply defined opening. 

 This occurs on the skin close to its junction with the mucous membrane, 

 and is the opening of the duct by which tears are drained from the eye. 



M. ZYGOMATICUS. — The zygomatic muscle is a thin, narrow band of 

 rather pale fibres that spring from the facial crest of the maxilla and 

 the masseteric fascia, and blend with the buccinator muscle at the 

 angle of the mouth. 



M. NASOLABIALIS. — The naso-labial muscle is flattened and thin, and 

 will be found immediately underneath the skin running in an oblique 

 direction from an area medial to the eye to the side of the nose and the 

 upper lip. Its origin is from the galea aponeurotica over the frontal 

 and nasal bones. From this thin and not very definite origin the 

 muscle becomes somewhat thicker, and divides into two parts. The 

 dorsal portion ends in the upper lip and the lateral wing of the nostril 

 under cover of the m. caninus. The ventral part, somewhat narrower, 

 crosses the surface of the caninus muscle to end in the upper lip near 

 the angle of the mouth, where its fibres blend with those of the 

 orbicular and buccinator muscles, 



M. CANINUS. — The canine muscle is triangular in shape, and arises 

 by a thin, narrow tendon from the maxilla just anterior to the end of 

 the facial crest. The muscular fibres diverge as they pass between the 

 two parts of the naso-labial muscle, and end in the lateral ala of the 

 nostril, the wall of the diverticulum of the nostril and the upper lip. 



M. DEPRESSOR LABii INFERIORIS. — The origin (from the alveolar 

 border of the mandible and the maxillary tuber) and a considerable part 

 of this muscle cannot be examined as yet. Its rounded belly, however, 

 appears at the anterior margin of the masseter muscle and ends in a 

 rounded tendon about the level of the mental foramen of the mandible. 

 In the lower lip the tendon divides into bundles of fibres that are 

 connected with similar bundles of the tendon of the other side of the 

 head. 



There is a considerable amount of fusion between the belly of the 

 depressor and the buccinator. 



M. ORBICULARIS ORIS. — The sphincter muscle of the mouth consists 

 of fibres arranged parallel to the free edge of the lips and mingled with 

 fibres from the various muscles that end in the lips. It has no bony 

 attachments. The skin and mucous membrane of the lips are adherent 

 to the surface of the muscle. 



M. MASSETER. — The powerful masseter muscle lies over the outer 



