116 OUTLINES OF EQUINE ANATOMY. 



portions by the passage of the insertion portion of retractor 

 labii superioris, which spread out in their course towards 

 the ala of the nostril and the upper lip, while their origin 

 from the superior maxillary bone in front of the termina- 

 tion of the zygomatic ridge is hidden by zygomaticus. 



Extending round the free margin of the lips are a number 

 of fibres of red muscular substance into which all the mus- 

 cles running to these organs seem to pass ; this is orbicu- 

 laris oris, the muscle by which the lips are closed and the 

 animal enabled to grasp small articles (as oat grains) on a 

 flat surface. This muscle is nowhere intimately attached 

 to the bone, but is composed of a series of short fibres 

 encircling the oral opening. 



The frontal and nasal bones are immediately in contact 

 with the skin on the forehead and nose, but about opposite 

 to the nasal peak the tendon of nasalis longus labii 

 superioris emerges from beneath lev. labii sup. alseque 

 nasi, and running over the cartilaginous prolongation of 

 the nasal bones, where it is lubricated with synovia, it gains 

 the anterior surface of the alse of the nostril, which are 

 here to be seen covered by dilator naris anterior (which 

 runs from the external surface of one ala to that of the 

 other) ; here the tendon blends with the corresponding 

 tendon from the other side of the face, and from the point 

 of union the fibres radiate to blend with orbicular oris, and 

 become inserted into the skin of the upper lip. 



The false nostril fills the angle formed between this 

 tendon and the levator labii sup. alseque nasi. From the 

 anterior edge of the nasal bones, extending as far back as 

 where this bone meets the anterior maxillary bone, the 

 dilator naris superior arises, and runs to be inserted into 

 the false nostril along its whole superior margin. 



Below retractor anguli oris the terminal portion of 

 retractor labii inferioris with a small round tendon is 

 found going to blend with orbicularis oris in the lower lip 

 (this tendon is connected to the inferior maxillary bone 

 below the corner incisor by a distinct band of muscular 

 fibres in some subjects), and below this the bone is sub- 

 cutaneous. 



On removal of the superficial muscular layer of the face 

 we expose the masseter externus, a huge square mass of 

 muscle arising along the whole length of the under surface 

 of the zygomatic process, and passing to the whole external 



