12Q OUTLINES OF EQUINE ANATOMY. 



ture, and mucous membrane, witli veins, arteries, lymph- 

 atics, and especially nerves, the large size of which renders 

 the " twitch " such an effectual " sedative ?" It is orbi- 

 cularis oris which forms the greater part of the lij^s, and 

 which brings the two lips into close connection at their 

 extremities, whereby the commissures, or angles of the mouth, 

 are formed. The lips are the organs of prehension of the 

 horse, and present an external surface from which long 

 hairs, ''feelers,'' project, more especially from the inferior 

 central prominent portion commonly called the chin. The 

 internal surface of the lips is concave, moulded upon the 

 anterior surfaces of the inferior and anterior maxillary 

 bones (which is covered by the dense mucous membrane 

 which forms the gum) and upon the anterior surfaces of 

 the crowns of the incisors. The free margins of the lips 

 are in contact with each other, or sej^arated according as 

 the mouth is shut or open. 



The remainder of the skin may now be removed, when 

 another orbicularis muscle will be exposed in the eyelids, 

 which it tends to approximate and to maintain in appo- 

 sition. This is orbicularis palpebrarum, which is attached 

 by a small tendon to the lachrymal tubercle situated on 

 the facial surface of the lachrymal bone. Its fibres extend 

 into the upper and the lower lids, and meet at the o^der 

 angle, commissure, or canthus of the eye. It is exter- 

 nally in contact with the skin, which is thin and smooth 

 in this neighbourhood. Internally it is fixed to the bones 

 which form the rim of the orbit by loose areolar tissue, 

 and in the substance of the upper eyelid is attached to 

 the tarsal cartilage or ligament, a small semilunar portion 

 of yellow elastic cartilage which is thickest in the centre, 

 and grows narrower and thinner until it terminates in a 

 point at either extremity in becoming continuous with the 

 white fibrous tissue of the eyelid. It is sometimes found 

 in the lower lid, but is then mostly fibrous. On the 

 internal SLirface of this cartilage, and running in small 

 parallel lines visible through the mucous membrane lining 

 the eyelid, in a direction perpendicular to its free margin, 

 are the meibomian glands, specially modified sebaceous 

 glands, the product of which serves to prevent overflow 

 of tears on to the external surface of the lids. To orbi- 

 cularis palpebrarum run several muscles. 



Levator palpebrae superioris externus runs from the 



