170 MYOLOGY. 



DIGASTRICUS. 



Situated along the inner surface of the lower jaw, in the 

 maxillary space, it contains two fleshy bellies, united by a 

 median tendon. 



Origin. — From the styloid process of the occipital bone. 



Insertion. — By a diffused tendon to the inner surface of the 

 lower jaw, towards its symphysis; the mesian tendon plays 

 through a groove formed by the tendon of the hyoideus magnus, 

 at the body of the hyoid bone. The posterior, belly gives off 

 also a bundle which is inserted to the posterior border of the 

 ramus, considerably above the angle. 



Action. — It elevates the hyoid bone, retracts and depresses 

 the inferior maxilla. 



Hyoidean Group. 



The muscles of this group are six in number and they act 

 chiefly upon the hyoid series of bones. Their names are as 

 follows : — 



Mylo-hyoideus. 

 Genio-hyoideus. 

 Hyoideus magnus. 



Hyoideus parvus. 

 Hyoideus transversus. 

 Stylo-byoideus. 



MYLO-HYOIDEUS. 



Situated in the maxillary space, along the inner side of the 

 lower jaw, it is broad, flat, and penniform, and attached to a line 

 running along the inferior maxiUa, just below the alveolar pro- 

 cesses ; extending forwards as far as the symphysis, and to the 

 inferior surface of the body and spur process of the hyoid bone, 

 it meets its fellow of the opposite side in the median, line. 



Relation. — Externally with the inferior maxilla, the digastri- 

 cus and the lymphatic glands ; internally with the sublingual 

 gland, Wharton's canal, the genio-hyoideus, hyo-glossus longus, 

 genio-hyo-glossus, and the hypoglossal and lingual nerves ; 

 posteriorly with the pterygoidei-muscles. 



Action. — By drawing the os hyoides upwards and forwards it 

 elevates the tongue, forming a kind of muscular sling in which 

 the latter organ lies. 



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