194 ANATOMY OF THE HEAD. 



to the substance of the under lip. This muscle would pull 

 backward the under lip. Orbicularis oris (Plate 11. 11), 

 a sphinctor, of use to close the lips. Its fibres encircle the 

 opening of the mouth. Levator labii inferioris serves 

 to draw upward, and to render firm the under lip. Origi- 

 nates. From the incisor alveolars of the lower jaw. Inserted. 

 Into the rudimental chin of the horse. 



Whoever studies the forementioned muscles will find 

 ample cause for the varied movements of the lips ; more 

 especially when he considers that the anatomist deals only 

 with a dead body, and thus makes an entire muscle act at 

 once to determine its action ; whereas it is not unnatural to 

 imagine that in a living state muscular fibres do not all act 

 at once, but each has a separate and distinct movement ; 

 whereby the motions of the lips would be varied and mul- 

 tiplied almost beyond the power of human calculation. 



The lips of the horse are to that animal the prehensile 

 organ, as any one may ascertain who observes a horse feed 

 at grass. The food is then collected with the lips ; and so 

 accurate is the sense of touch which resides in them, aided 

 by the smell, that all poisonous plants are rejected, and 

 only the nicest morsel chosen. The most sensitive part in 

 the body of the horse is the upper lip ; a fact unfortunately 

 too well known to grooms and farriers, who on every 

 occasion place a twitch on the tender part, and by screwing 

 it tight render the animal afraid to move. 



The arteries which supply the internal parts of the mouth 

 are the inferior and superior maxillaries, after they pass 

 through the foramina in the upper and lower jaws. The 

 facial artery, — a portion by the lateral nasal, — the infra 

 orbital, &c., so that they are amply supplied with blood. 

 Their nervous sensibility and sense of touch is imparted by 

 the superior maxillary branch of the fifth nerve. The 

 motion is derived from the portio dura or facial nerve. 



Now let us investigate the interior of the mouth. The 

 gu7ns are formed of a very vascular compact and elastic 

 substance completely surrounding the neck of each tooth ; 

 and, as this substance is also adherent to the periosteum, 

 so it supports the teeth firmly in their situations {Plate 

 VII. c). They are far more vascular than sensitive, and 

 appear to be formed by cellular tissue amply supplied with 



