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MUSCLES AND FASCIAE. 



By its internal surface, with the Tensor Palati, being separated from the Superior 

 Constrictor of the pharynx by a cellular interval. 



The External Pterygoid is a short thick muscle, somewhat conical in form, 

 which extends almost horizontally between the zygomatic fossa and the condyle 

 of the jaw. It arises from the pterygoid ridge on the great wing of the sphe- 

 noid, and the portion of bone included between it and the base of the pterygoid 

 process; from the outer surface of the external pterygoid plate; and from the 

 tuberosity of the palate and superior maxillary bones. Its fibres pass horizon- 

 tally backwards and outwards, to be inserted into a depression in front of the 

 neck of the condyle of the lower jaw, and into the corresponding part of the 

 iuterarticular fibre-cartilage. This muscle, at its origin, appears to consist of 

 two portions separated by a slight interval; hence the terms upper and lower 

 head sometimes used in the description of the muscle. 



Relations. By its external surface, with the ramus of the lower jaw, the in- 

 ternal maxillary artery, which crosses it, 1 the tendon of the Temporal muscle, 

 and the Masseter. By its internal surface, it rests against the upper part of the 

 Internal Pterygoid, the internal lateral ligament, the middle meningeal artery, 

 and inferior maxillary nerve ; by its upper border it is in relation with the tem- 

 poral and masseteric branches of the inferior maxillary nerve. 



Nerves. These muscles are supplied by the inferior maxillary nerve. 



Actions. The Temporal, Masseter, and Internal Pterygoid raise the lower 

 jaw against the upper with great force. The superficial portion of the Masseter, 

 and the Internal Pterygoid, assist the External Pterygoid in drawing the lower 

 jaw forwards upon the upper, the jaw being drawn back again by the deep 

 fibres of the Masseter, and posterior fibres of the Temporal. The External 

 Pterygoid muscles are the direct agents in the trituration of the food, drawing 

 the lower jaw directly forwards, so as to make the lower teeth project beyond 

 the upper. If the muscle of one side acts, the corresponding side of the jaw 

 is drawn forwards, and the other condyle remaining fixed, the symphysis 

 deviates to the opposite side. The alternation of these movements on the two 

 sides produces trituration. 



MUSCLES AND FASCLE OF THE NECK. 



The Muscles of the Neck may be arranged into groups, corresponding with 

 the region in which they are situated. 



These groups are nine in number : 



1. Superficial Region. 



2. Depressors of the Os Hyoides 



and Larynx. 



3. Elevators of the Os Hyoides 



Depressors of the Lower Jaw. 



4. Muscles of the Tongue. 



5. Muscles of the Pharynx. 



1. Superficial Cervical Region. 

 Platysma Myoides. 

 Stcrno-cleido-mastoid. 

 Mylo-hyoid. 

 (irnio-hyoid. 



2. Infra-ltyoid Region. 



6. Muscles of the Soft Palate. 



7. Muscles of the Anterior Verte- 



bral Region. 



8. Muscles of the Lateral Vertebral 



Region. 



9. Muscles of the Larynx. 



Sterno-thyroid. 



Thyro-hyoid. 



Omo-hyoid. 



3. Supra-hyoid Region. 



Elevators of the Os Hyoides Depressors 



of the Lower Jaw. 



Depressors of the Os Hyoides and Larynx. Digastric. 

 Sterno-hyoid. Stylo-hyoid. 



1 This is the usual relation ; but in many cases the artery will be found below the muscle. 



