THE HEAD AND NECK. 



81 



3. Backward. The stylo-hyoid and digastric, when not antagonized by the 

 mylo-hyoid and genio-hyoid, pull the hyoid bone backward. 



4. Downward. The depressor muscles of the hyoid bone, when not antag- 

 onized, pull the hyoid bone down, and with it the tongue. The depressors of the 

 hyoid bone are the sterno-hyoid, omo-hyoid, sterno-thyroid, and thyro-hyoid 

 muscles. Their nerve-supply is from the ansa hypoglossal loop. 



Study the simple movements of the tongue and the muscles that produce 

 them. 



1 . Protrusion beyond the teeth = deep part of genio-hyo-glossus. 



2. Retraction = superficial part of genio-hyo-glossus. 



3. Convex dorsurn = hyo-glossi. 



4. Concave dorsum = inferior part of lingualis and stylo-glossus. 



5. Shorten tongue = the lingualis. 



SOCIA PAROTIDIS 



DUCT OF SOCIA 

 PAROTIDIS 



DUCT OF PAROTID 



Bristle inserted 

 into duct 



Fraenum linguae 

 DUCT OF RIVINI 



SUBLINGUAL GLAND 



DUCT OF SUBMAXILLARY 



GLAND 

 Mylo-hyoid muscle 



Anterior belly of 

 digastric muscle 



PAROTID GLAND 



Masseter muscle 



Sterno-mastoid 

 muscle 



Posterior belly of 

 digastric muscle 



SUBMAXILLARY GLAND, 

 DRAWN BACKWARDS 



Loop of fascia 



DESP PORTION OF SUBMAXILLARY GLAND 

 FIG. 45. SIDE OF THE FACE AND MOUTH CAVITY, SHOWING THE THREE SALIVARY GLANDS. 



There may be a great number of compound movements. Thus, the tongue 

 may be concave-dorsum, in protrusion or retraction ; convex-dorsum, the same. 

 In any of the foregoing positions the whole organ may be turned to either side, 

 or the base may be elevated. 



Divide the connective tissue between the genio-hyoid and genio-hyo-glossus. 

 (Fig. 44.) The genio-hyoid arises from the inferior genial .tubercle of the 

 mandible. (Fig. 9.) It is inserted into the body of the hyoid bone. 



The genio-hyo-glossus arises from the superior genial tubercle. (Fig. 9.) 

 It has a superficial insertion into the anterior part of the tongue ; a deep inser- 

 tion into the body of the hyoid ; above the preceding, of course. This muscle 

 produces the rapid protrusion and retraction of the tongue. 



The mylo-hyoid muscle forms the floor of the mouth. Divide the con- 

 nective tissue between it and the genio-hyoid. (Fig. 44.) This muscle arises 

 from the oblique line of the mandible the mylo-hyoid ridge. (Fig. 9.) A 



