218 FASCIA AND MUSCLES OF THE HORSE 



Structure. — It is composed of transverse fleshy fibers, which blend below with 

 the orbicularis. 



Relations. — Superficially, the skin, fascia, and tendinous expansion of the 

 levator labii superioris proprius; deeply, the alar cartilages, the extremity of the 

 septum nasi, and the palato-labial artery. 



Blood-supply. — Palato-labial artery. 



Nerve-supply. — Facial nerve. 



4. Dilatator naris superior (Pars dorsalis m. lateralis nasi) .^This very thin 

 muscle occupies the angle between the nasal process of the premaxilla and the 

 nasal bone. 



Origin. — The lateral border of the nasal bone. 



Insertion. — The inner wall of the false nostril and the parietal lamina of the 

 septal cartilage. 



Action. — To dilate the vestibule of the nasal cavity. 



Struct ure. — Fleshy. 



Relations. — Superficially, the skin, fascia, and levator labii superioris proprius; 

 deeply, the parietal cartilage and false nostril. 



Blood-supply. — Facial artery. 



Nerve-supply. — Facial nerve. 



5. Dilatator naris inferior (Pars ventralis m. lateralis nasi) .--This is a similar 

 but thicker muscle, which lies on the nasal process of the premaxilla. 



Origin. — The maxilla and the nasal process of the premaxilla. 



Insertion. — The cartilaginous prolongations of the turbinal bones and the 

 inner wall of the false nostril. 



Action. — To rotate the turbinal outward and dilate the nostril and the vestibule 

 of the nasal cavity. 



Structure. — Fleshy. A division into two or more parts may be recognized. 

 A small part posteriorly is inserted into the cartilage of the dorsal turbinal bone, 

 while the bulk of the muscle is inserted into the cartilage of the ventral turbinal 

 bone. A few fibers also pass between the cornu of the alar cartilage and the outer 

 wing of the nostril. 



Relations. — Superficially, the levator labii superioris proprius, the levator 

 nasolabialis, and the lateral nasal artery; deeply, the maxilla, the premaxilla, and 

 the anterior nasal branch of the infraorbital nerve. 



Blood-supply. — Facial artery. 



Nerve-supply. — Facial nerve. 



MUSCLES OF THE EYELIDS 



1. Orbicularis oculi. — This is a flat, elliptical, sphincter muscle, situated in and 

 around the eyelids, the portion in the upper lid being much broader than that in 

 the lower. The chief attachment is to the skin of the lids, but some bundles are 

 attached to the palpebral ligament at the inner canthus and to the lacrimal bone. 

 Its action is to close the lids. 



2. Corrugator supercilii. — This is a very thin, small muscle, which arises over 

 the root of the supraorbital process and spreads out in the ujiper eyelid, blending 

 with the orbicularis. Its action is to assist in raising the upper lid or, especially 

 in pathological conditions, to wrinkle the skin. 



3. Malaris. — This is a very thin muscle, which varies much in different sub- 

 jects. It extends from the fascia in front of the orl)it to the lower lid. Its action 

 is to depress the lower lid. 



The foregoing muscles receive their blood-supply from the facial, transverse 

 facial, supraorbital, and infraorbital arteries; the nerve-supply is derived from the 

 facial nerve. 



