THE MUSCLES OF THE HEAD. 107 



Origin from tlie pad upon which the whiskers rest. The 

 fibres diverge and have their 



Insertion upon the wing of the nose and into the skin of the 

 upper h"p near the median line. 



Action. — Dilator of the nares and elevator of the upper lip. 



M. *' moustachier " (Str.-D.) (probably corresponds to 

 one of the Mm. incisivi). — It lies on the upper lip near the 

 median line. 



Origin from the outer surface of the premaxilla near the 

 suture along the ventral border of the narial opening. The 

 fibres diverge and pass caudad into the upper lip within the 

 superficial fibres of the orbicularis oris. 



Insertion. — The skin of the upper lip just craniad of the 

 whiskers. Some of the fibres pass into the pad on which the 

 whiskers rest. 



Action. — It carries the lip craniad. 



M. quadratus labii inferioris. — A thin flat band extending 

 almost the length of the lower lip. 



Origin from the alveolar border of the mandible, between 

 the molar tooth and the canine. The fibres pass dorsad into 

 the lower lip, where they intermingle with those of the orbi- 

 cularis oris. The muscle is perhaps not constant. 



Action. — Depressor of the lower lip. 



Sometimes a few fibres arising from the cranial portion of 

 the alveolar border of the mandibula pass mediad, seeming to 

 join corresponding fibres from the opposite side. Such fibres 

 would constitute a M. transversus menti. 



B. Deep Muscles of the Head.. 

 {a) Muscles of Mastication. 



M. digastricus (Fig. 65, /;). — The digastric is a thick pris- 

 matic muscle lying mediad of the angle of the lower jaw, con- 

 necting it with the base of the skull. 



Origin by fleshy fibres from the outer surface of the jugular 

 process of the occipital bone, and by a thin tendon from the 

 tip of the mastoid process and from the ridge between the 

 mastoid and the jugular processes. The muscle passes craniad, 

 becoming at the same time broader and more voluminous. 



