224 THE 31VSCLES. 



bony crests which margin it ; 2, By a wide fasciculus, paler than the other 

 portion of the muscle, but not unconnected with it, from the imprints 

 situated behind the crest surmounting the orbital hiatus. It terminates on 

 the coronoid process and the anterior border of the branch of the lower 

 jaw. 



delations. — This muscle covers the temporal fossa, and is covered by the 

 temporo-auricularis muscles, scutiform cartilage, internal scuto-auricularis, 

 the fatty cushion at the base of the ear, and by another adipose mass which 

 separates it from the ocular sheath. Its deep fasciculus responds, by its 

 internal face, to the two pterygoid muscles. 



Action. — It brings the lower jaw in contact with the upper, by acting as 

 a lever of the first kind ; but the orbital portion of the muscle elevates the 

 inferior maxilla and moves it laterally by a lever of the third class. 



3. Internal Pterygoid. 



Synonyms. — Portion of the spheno-maxillaris of Bourgelat. (The pterygoideus mternus 

 of Peroivall. Leyh designates the pterygoideus internus and externus as one muscle, the 

 spheno-maxillaris or internal masseter.) 



Situation — Form — Structure. — Situated in the intermaxillary space, 

 opposite the masseter, the pterygoideus internus, although not so strong as 

 that muscle, yet so closely resembles it in form and structure as to be 

 named by Winslow the internal masseter. 



Attachments. — 1. To the palatine crest and subsphenoidal process — fixed 

 insertion : 2. In the hollow excavated on the inner face of the branch of the 

 lower jaw — movable insertion. 



Belations. — Outwardly, with the pterygoideus-externus, the orbital 

 fasciculus of the temporal, the maxillo- dental nerves, mylo-hyoideal, and 

 lingual muscles, arteries and veins, and the inner surface of the bone which 

 receives its movable insertion. Inwardly, with the tensors palati — external 

 and internal, the guttural pouch, the hyoideus magnus, hyoid bone, digastricus, 

 the hypoglossal and glosso-pharyngeal nerves, glosso-facial artery and vein, 

 the hyoglossus longus and brevis muscles, the laryngo-pharyngeal apparatus, 

 the Stenonian duct, and the submaxillary glands. 



Action. — It is an elevator of the lower jaw, and also gives it a very 

 marked lateral' or deductive motion. If the left muscle acts, this movement 

 carries the inferior extremity of the lower jaw to the right ; and if it be 

 the right muscle, then in the contrary direction. 



4. External Pterygoid. 

 Synonym. — Portion of the Bpheno-maxillaris of Bourgelat. 



Form — Situation — Structure — Attachments. — A small, short, and very 

 thick muscle, situated within and in front of the temporo-maxillary 

 articulation, formed of slightly tendinous fasciculi which leave the inferior 

 face of the sphenoid bone and the subsphenoidal process, and are directed 

 backwards and upwards to be fixed to the neck of the inferior maxill iry 

 condyle. 



Belations. — Outwardly, with the orbital fasciculus of the temporal 

 muscle, and the temporo-maxillary articulation. Inwardly, with the 

 numerous nerves emanating from the inferior maxillary branch, and with 

 the internal pterygoid and tensors palati. 



Action. — When the two external pterygoids act in concert, thAiferior 

 maxilla is pulled forward; but if only one contract, the propMpi is 



