260 FASCIiE AND MUSCLES OF THE HORSE 



the dorsal border of the naso-maxillary notch. Its fibers arise from the nasal bone 

 and pass outward and downward to the parietal cartilage and the adjacent part of 

 the soft lateral wall of the nasal cavity. 



The ventral part (Pars ventralis m. lateralis nasi)^ is much thicker and lies 

 along the ventral border of the notch. It arises from the nasal process of the pre- 

 maxilla and the adjacent part of the maxilla, and its fibers curve inward to end on 

 the cartilaginous prolongations of the turbinate bones (chiefly the ventral one) and 

 on the lateral wall of the vestibule of the nasal cavity. A few bundles pass from 

 the cornu of the alar cartilage to the lateral wing of the nostril. 



Action. — To dilate the vestibule of the nasal cavity, to rotate the turbinal car- 

 tilages outward, and to assist in dilating the nostril. 



Relations. — Superficially, the skin, fascia, nasal diverticulum, the levator labii 

 superioris proprius, the levator nasolabialis, and the lateral nasal arterj^; deeply, 

 the nasal bone, the parietal cartilage, the maxilla, the premaxilla, the nasal mucous 

 membrane, and the anterior nasal branch of the infraorbital nerve. 



Blood-supply. — Facial and palato-labial arteries. 



Nerve-supply. — Facial nerve. 



The preceding muscle does not dilate the so-called "false nostril" or nasal diverticulum, as 

 is commonly stated. Both act on the lateral wall of the vestibule of the nasal cavity so as to draw 

 it outward, thus tending to constrict, rather than dilate, the nasal diverticulum. The thick part 

 of the ventral muscle which is attached to the cartilage of the turbinate bone has a similar effect. 

 When the nostril is fully dilated, the so-called "false nostril," i. e., the entrance to the nasal diver- 

 ticulum, is closed. The newer term seems preferable. 



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 df the lids, but some bundles are 

 attached to the palpebral ligament at the medial 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 upper eyelid, blending 

 with the orbicularis ocuh (Fig. 262) . Its action is to assist in raising the upper hd 

 or, especially in pathological conditions, to wTinkle 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 orbit to the lower lid. Its action 

 is to depress the lower lid. 



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

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

 facial nerve. 



4. Levator palpebrae superioris. — This slender, flat muscle is almost entirely 

 within the orbit (Fig. 561). It arises on the pterygoid crest, passes forward above 

 the rectus oculi superior and below the lacrimal gland, and terminates in a thin ten- 

 don in the upper lid. 



Action. — To elevate the upper lid. 

 Blood-supply. — Ophthalmic artery. 

 Nerve-supply. — Oculomotor nerve. 



MANDIBULAR MUSCLES 



The muscles of this group (Mm. mandibulse) are six in number in the horse. 

 They arise from the upper jaw and the cranium, and are all inserted into the man- 

 dible. 



^ Also known as the dilatator naris inferior. 



