I1YOID AND STYLOID MUSCLES. 99 



tight the muscular fibres. All the fat and areolar tissue are to be removed, 

 and in doing this the student is to take care of the Whartonian duct ; of 

 the hypoglossal nerve and its brandies, which lie on the hyo-glossus mus- 

 cle, and especially of its small offset ascending to the stylo-glossus mus- 

 cle ; also of the gustatory nerve nearer the jaw. Between the gustatory 

 nerve and the deep part of the submaxillary gland the dissector should 

 seek the small submaxillary ganglion (smaller than a pin's head), with 

 its offsets; and should endeavor to separate from the trunk of the gustatory 

 the small chorda tympani nerve, and to define the offset from it to the 

 submaxillary ganglion. 



At the hinder border of the hyo glossus clean the lingual vessels, the 

 stylo-hyoid ligament, and the glosso-pharyngeal nerve, all passing beneath 

 that muscle; and at the anterior border find the issuing ranine vessels 

 which, with the gustatory and hypoglossal nerves, are to be traced on the 

 under surface of the tongue to the tip. 



Parts beneath mylo-hyoideus (fig. 23). The relative position of the 

 objects brought into view by the steps of the previous dissection is now 

 apparent: Extending from the cornu of the hyoid bone to the side of the 

 tongue is the hyo-glossus muscle, whose fibres are crossed superiorly by 

 those of the stylo-glossus. On the hyo-glossus are placed, from below 

 upwards, the hypoglossal nerve, the Whartonian duct, and the gustatory 

 nerve, the latter crossing the duct; and near the inner border of the mus- 

 cle the two nerves are united by branches. Beneath the same muscle lie, 

 from below upwards, the lingual artery with its vein, the stylo-hyoid 

 ligament, and the glosso-pharyngeal nerve. Above the hyo-glossus is the 

 mucous membrane of the mouth, with the sublingual gland attached to it 

 in front, and some fibres of the superior constrictor muscle covering it 

 behind near the jaw. 



Between the chin and the os hyoides, along the middle line, is situate 

 the genio-hyoid muscle ; and larger and deeper than it is a fan-shaped 

 muscle, the genio-hyo-glossus. Along the outer side of the last muscle lie 

 the ranine vessels ; and a sublingual branch for the gland of the same 

 name springs from the lingual artery at the inner border of the hyo-glos- 

 sus. On the under surface of the tongue, near the margin, lies the gus- 

 tatory nerve. ; and in the fibres of the genio-hyo-glossus runs the hypo- 

 glossal nerve. 



The HYO-GLOSSDS MUSCLE (fig. 22, ') is thin and somewhat square in 

 shape. The muscle arises from the lateral part of the body of the os 

 hyoides (basio-glossus), and from all the great cornu of the same bone 

 (cerato-glossus). The two pieces form a thin sheet, and enter the back 

 part and side of the tongue ; they will be seen afterwards to mingle with 

 fibres of the palato- and stylo-glossus. 1 



The parts in contact with the surfaces of the hyo-glossus have been 

 already enumerated ; and beneath the muscle also are portions of the 

 genio-hyo-glossus and middle constrictor. Along the anterior border is 

 the genio-hyo-glossus muscle. 



Action. When the tongue is at rest, the muscle can bring that organ 

 to the floor of the mouth, drawing down the sides and giving a rounded 



1 A third part (chondro-glossus) is distinct from the others, and is not dissected ; 

 it ends on the upper surface of the tongue near the root. For further details re- 

 specting the anatomy of this aud the other lingual muscles, reference is to be made 

 to the dissection of the tongue, SECTION 15. 



