190 THE ANATOMY OF THE HORSE. 



Action. — The principal action of the muscle is to elevate the lower 

 jaw directly, the two muscles acting together; but acting singly or 

 alternately they assist in producing lateral movement. 



The Temporal Muscle occupies the fossa of the same name. Its 

 fibres arise from the parietal, frontal, and squamous temporal bones 

 where they bound this fossa, and from the sphenoid bone above the 

 orbital hiatus. They become inserted into the coronoid process and 

 adjacent part of the anterior border of the vertical ramus. 



Action. — Chiefly to elevate the low T er jaw, acting in conjunction with 

 the masseter and internal pterygoid. The temporals also oppose the 

 action by which the external pterygoids protrude the lower incisors in 

 front of the upper. 



Directions. — Emerging at the line of apposition of the two pterygoid 

 muscles are the inferior dental vessels and nerve, the mylo-hyoid nerve, 

 the internal maxillary vein, and the lingual branch of the 5th nerve. 

 These are now to be examined. 



The Inferior Dental Artery (Plate 30) is a branch of the internal 

 maxillary, detached before that vessel enters the subsphenoidal canal. 

 It passes first between the two pterygoid muscles, and then between the 

 inner muscle and the bone, and enters the inferior dental canal of the 

 inferior maxilla. On examining the inner aspect of the vertical ramus, 

 the truncated end of the vessel will be seen at the upper orifice of the 

 canal. It is continued in the bone beneath the molar, canine, and 

 incisor teeth ; supplying these, and detaching at the mental foramen a 

 mental branch. 



The Inferior Dental Vein (Plate 30) has a distribution similar to 

 that of the artery which it accompanies, and it joins the internal 

 maxillary vein. 



The Inferior Dental Nerve (Plate 30) is a branch of the inferior 

 maxillary division of the 5th nerve. It accompanies the vessels in the 

 bone, supplying the teeth, and detaching sensory mental branches to 

 the lower lip. 



The Mylo-Hyoid Nerve (Plate 30) is a branch of the preceding nerve. 

 It descends between the internal pterygoid muscle and the bone, and 

 reaches the intermaxillary space. There it has already been dissected 

 on the surface of the mylo-hyoid muscle, to which and the lower belly 

 of the digastricus it is distributed. 



The Lingual or Gustatory Nerve (Plate 30) is a large branch of 

 the inferior maxillary division of the 5th. Between the two pterygoid 

 muscles it is joined by the chorda tympani branch of the 7th nerve, 

 and it is continued between the internal pterygoid and the bone to 

 reach the tongue. It will be followed in the dissection of that 

 organ. 



The Internal Maxillary Vein (Plate 30) lies in front of the pre- 



