442 



THE MUSCLES 



Nerve-supply. — The two or three deep temporal branches of the motor portion 

 of the niandibular division of the fifth nerve, -which enter the lower part of its deep 

 surface. 



Action. — To close tlie jaw: its posterior tilnvs will also draw it backwards after 

 the other muscles have protruded it. This muscle, like the masseter, has to con- 

 tend with very little mechanical disadvantage, power being of more importance in 

 mastication than speed. 



Fig. 312.— The Temporal Muscle. 



Temporal 



Relations. — Superficially, the temporal fascia which separates it from some of 

 the auricular muscles, the sides of the epicranial aponeurosis, the auriculo-temporal 

 nerve, and the upper branches of the facial nerve; the zygoma and a small part of 

 the masseter. Deeply, the temporal fossa, and the external pterygoid muscle. 



At its posterior border it is crossed by the masseteric nerve and vessels. 



3. PTERYGOIDEUS EXTERXUS 



The pterygoideus externus — named from its attachment to the pterygoid 

 process of tlie sphenoid bone, and its relation to the companion muscle — consists of 

 two thick triangular sheets, the one lying in a horizontal, and the other in a vertical 

 plane. 



Origin. — Upper head : the under surface of the great wing of the sphenoid 

 bone, internal to the jitcrvgoid ridge, and external to the foramen ovale and 

 foramen spinosum. Lower head : All the outer surface of the external i:)tervgoid 

 plate. 



Insertion. — Upper head : (1) The front of the interarticular fibro-cartilage of 

 the temporo-mandibular joint; (2) the adjacent portion of the capsular ligament; 

 (8 ) the upper part of the front of the neck of the condyle of the mandible. Lower 

 head : The pit in the front of the neck of the condyle. 



Structure. — Arising by fleshy fibres, which are closely connected at the ptery- 

 goid ridge with part of the temporal muscle, the upper head forms a fan-shaped 

 sheet and passes backwards and slightly outwards to its insertion, which is by 

 short tendinous fibres blending below with those of the lower head. The lower 



