258 FASCIAE AND MUSCLES OF THE HORSE 



Insertion. — The alveolar border of the mandible from the second incisor to a 

 point near the first cheek tooth. 



Insertion. — The skin of the lower lip and the prominence of the chin. 

 Action. — To raise the lower lip. 



7. Mentalis.' — This is situated in the prominence of the chin. Its fibers arise 

 from each side of the body of the mandible and are inserted into the skin of the 

 chin. It is mingled with fat and strands of connective tissue, in which the roots 

 of the tactile hairs are embedded. It raises and corrugates the skin to which it is 

 attached. 



8. Depressor labii inferioris. — This muscle lies on the lateral surface of the 

 ramus of the mandible, along the ventral border of the buccinator. 



Origin. — The alveolar border of the mandible near the coronoid process and 

 the maxillary tuberosity, in common with the buccinator. 



Insertion. — The lower lip. 



Action. — To depress and retract the lower lip. 



Structure. — The tendon of origin and the belly are fused with the buccinator 

 as far forward as the first cheek tooth. From this point forward the belly is dis- 

 tinct and rounded, terminating in a tendon which spreads out in the lower lip, 

 blending with the orbicularis and the muscle of the opposite side. 



Relatio7is. — Superficially, the skin, masseter, facial vessels, and parotid duct; 

 deeply, the mandible and inferior labial artery. 



Blood-supply. — Facial artery. 



Nerve-supply. — Facial nerve. 



9. Buccinator. — This niuscle lies in the lateral wall of the mouth, extending 

 from the angle of the mouth to the maxillary tuberosity. 



Origin. — The lateral surface of the maxilla above the interalveolar space and 

 the molar teeth; the alveolar border of the mandible at the interalveolar space and 

 also posteriorly where it turns upward to the coronoid process; the pterygo-mandib- 

 ular raphe. 



Insertion. — The angle of the mouth, blending with the orbicularis oris. 



Action. — To flatten the cheeks, thus pressing the food between the teeth; 

 also to retract the angle of the mouth. 



Structure. — Two layers may be recognized. The superficial layer (Pars buc- 

 calis) extends from the angle of the mouth to the masseter. It is incompletely pen- 

 nate, having a longitudinal raphe on which most of the muscle-fibers converge. 

 The upper fibers are directed chiefly downward and backward, the lower ones up- 

 ward and backward. The deep layer (Pars molaris) cojasists mainly of longitudinal 

 fibers. It blends in part with the superficial layer of the orbicularis; it has a 

 small tendinous attachment to the coronoid process behind, and is united ventrally 

 with the depressor labii inferioris. 



Relations. — Superficially, the skin and fascia, the zygomaticus, levator naso- 

 labialis, lateral dilator of the nostril, the superior buccal glands, the parotid duct, 

 the facial vessels, and branches of the facial nerve; deeply, the mucous membrane 

 of the mouth and the inferior buccal glands. 



Blood-supply. — Facial and buccinator arteries. 



Nerve-supply. — Facial nerve. 



MUSCLES OF THE NOSTRILS 



1. Levator nasolabialis. — This has been described (p. 255). 



2. Dilatator naris lateralis (M. caninus). — This thin, triangular muscle lies 

 on the lateral nasal region, and passes between the two branches of the levator 

 nasolabialis. 



' Also known as the levator menti. 



