304 



ORGANS OF DEGLUTITION. 



Digastricus Musdefa, twice, ywrcp, belly.) This mus- 

 cle is composed of two fleshy bellies, an anterior and poste- 

 rior, with a round tendon in the centre. It is situated 

 below the base of the lower jaw, at the anterior and lat- 

 eral portions of the neck. It arises from the groove on the 

 inner side of the mastoid process of the temporal bone, 

 descends fleshy, obliquely forwards and inwards, till it ap- 

 proaches the os-hyoides, when it becomes tendinous, per- 

 forates the stylo-hyoid muscle, connects itself by a strong 

 fascia sometimes by a ring-like pully to the hyoid bone, 

 FIG. 86. and then passes for- 



ward again fleshy, 

 forming the anterior 

 belly, to be inserted 

 into a depression, 

 close to the sym- 

 physis, on the in- 

 ner side of the lower 

 jaw. 



Function. To draw 

 down the lower jaw, 

 and to elevate the 

 os-hyoides, tongue 

 and larynx, when 

 the mouth is closed. 

 When the anterior belly acts it can draw these parts for- 

 wards. When the posterior acts they are drawn backwards. 

 It exerts, by these varied actions, great influence over 

 deglutition. 



Mylo-Jiyoideus , (/u&.q, a molar or grinder,) Fig. 86, is a 

 broad, triangular muscle, forming the floor of the mouth, 



FIG. 86 represents the muscles at the base of the lower jaw, and upper and 

 front part of neck. 1 Posterior belly of the digastricus. 2 Its anterior belly 

 3 Ligamentous loop through which it plays. 4 Stylo-hyoideus. 5 Mylo- 

 hyoideus. 6 Genio-hyoideus. 7 Tongue. 8 Hyo-glossus. 9 Stylo-glossus. 

 10 Stylo-Pharyngeus. 11 Sterno-cleido-mastoideus. 12 Its sternal origin. 13 

 Clavicular attachment. 14 Sterno-hyoideus. 15 Sterno-thyroideus. 16 Thyro- 

 hyoideus. 17 Anterior belly of omo-hyoideus. 18 Posterior belly of omo- 

 hyoideus. 19 Anterior edge of trapezius. 20 Scalenus anticus. 21 Scalenus 

 posticus. 22 Scalenus medius. 



