2iluscles of the Head. 



249 



Pars basilaris 

 OSS. opcipitalis 

 (sawed through) 



Vomer 

 Fossa pterygoidea - 

 Caviim nasi 



Palatum durum 

 Hamulus pterygoideus 





Os temporale 

 (awed tiirough) 



Arcus zygomaticus 



Processus condyloideus 

 mandibulae 



M. pterygoideus externus 



M. masscter 



Eamus mandibulae 



M. pterygoideus intcrnus 



Corpus mandibulae 



295. Muscles of mastication on right side, 



viewed from behind and somewhat medianward. 

 (The posterior half of the skixll has been removed.) 



M. pterygoideus externus (see also Fig. 294). Form: triangular, thick. Position: 

 in the fossa infra temjioralis , covered lateralward by the m. temporalis, arcus zygomaticus and 

 m. masseter. Origin: by two heads; upper head: flat, from the crista infratemporahs and the 

 facies inft-a temporalis of the great wing of the sphenoid ; lower head : rounded, partly from the 

 lamina lateralis proc. pteiygoidei and from the processus pyramidalis oss. palatini, partly from 

 the tuber maxiUare. Insertion: the fibres run converging backward and lateralward to the 

 fovea pterygoidea proc. condyloidei mandibulae, partly also to the anterior surface of the capsula 

 articiilaris and of the discus artieularis of the joint of the lower jaw. Action: draws the 

 niandibula forward, the proc. condyloideus and discus artieularis under the tuberculum articulare; 

 when it acts on one side alone it draws it somewhat toward the other half of the body. 

 Innervation: pterygoideus externus (V. 3). 



M. pterygoideus internus (see also Fig. 294). Form: oblong -quadrangular, thick. 

 Position : on the medial side of the lower jaw, in a direction similar to that of the ra. masseter; it 

 is covered lateralward partly by the m. pteiygoideus externus, m. temporalis, ramus mandibulae 

 and m. masseter. Origin: fossa pterygoidea, by a small part also (lateralward fi'om the 

 m. pterygoideus externus) fi-om the corpus maxillae. Insertion: by parallel libres downward, 

 backward and somewhat lateralward to the medial surface of tbe angidus mandibulae and its 

 neighbourhood. Action: hfts the lower jaw; when it acts on one side only it draws the jaw 

 toward the opposite side of the body. Innervation: n. pterygoideus internus (V. 3). 



