100 



DISSECTION OF THE SUBM AXILLARY REGION. 



Fig. 22. 



form to the dorsum ; but if the tongue is protruded from the mouth, the 

 fibres will retract it into that cavity. 



If the tongue is fixed against the roof of the mouth by other mus- 

 cles, even though the lower jaw is depressed, this muscle with the genio- 

 hyo-glossus will elevate the os hyoides, and allow swallowing to take 

 place. 



The STYLO-GLOSSUS (fig. 22, 2 ) is a slender muscle, whose attachments 

 are expressed by its name. Arising from the styloid process near the 

 apex, and from the stylo-maxillary ligament, the muscle is continued for- 

 wards to the side of the tongue. Here it gives fibres to the dorsum, and 

 turning to the under surface, extends to the tip of the tongue. Beneath 

 the jaw this muscle is crossed by the gustatory nerve. 



Action. Both muscles will raise the back of the tongue against the 

 roof of the mouth, but if the tongue is protruded they will restore it to the 

 cavity. 



One muscle can direct the point of the tongue towards its own side of 

 the mouth. 



The GENIO-HYOID MUSCLE (fig. 22, 4 ) arises from the lower of the two 



lateral tubercles on the inner aspect of 

 the symphysis of the jaw, and is in- 

 serted into the middle of the hyoid 

 bone. 



Covered by the mylo-hyoideus, this 

 muscle rests on the genio-hyo-glossus. 

 The inner border touches the muscle of 

 the opposite side, and the two are often 

 united. 



Action. As long as the mouth is 

 shut it raises the hyoid bone ; but 

 acting from the os hyoides, and the 

 closers of the mouth being relaxed, it 

 can depress the jaw and open the 

 mouth. 



The GENIO-HYO-GLOSSUS (fig. 22, 3 ) 

 is the largest muscle of this region ; it 

 has a triangular form, with the apex 

 at the jaw, and the base at the middle 

 line of the tongue. It takes origin 

 from the upper tubercle behind the 

 symphysis of the jaw. From this spot 

 the fibres radiate, the posterior passing 

 downwards to their insertion into the 

 body of the hyoid bone, the anterior 



forwards to the tip of the tongue, and the intermediate to the tongue from 

 root to point. 



Lying along the middle of the tongue, it is in contact with its fellow. 

 The lower border of the muscle corresponds with the genio-hyoideus, and 

 the upper with the frzenum linguoB. On its outer side are the ranine ves- 

 sels, and the hyo-glossus muscle ; and the hypoglossal nerve perforates the 

 posterior fibres. 



Action. By the simultaneous action of all the fibres the tongue is 

 dtjjressed in the floor of the mouth, and hollowed along the middle. But 

 different parts of the muscle are thought to have different uses when they 



MUSCLES OF THE TONGUE. 



1. Hyo-glossus. 4. Genio-hyoideus. 



2. Stylo-glossus. 5. Stylo-pharyugeus. 



3. Genio-hyo-xlossus. 



