148 THE HEAD AND NECK 



in relation to it, will require excision, possibly with many 

 neighbouring structures. 



Portions of the submaxillary salivary gland may be removed 

 without the occurrence of a salivary fistula, which only follows 

 injury to the duct itself or to its larger tributaries. 



The Genio-hyoid is a narrow, strap-like muscle, which arises from the 

 lower part of the mental spine (genial tubercle), and is inserted into the hyoid 

 bone. It lies immediately under cover of the mylo-hyoid, and is supplied by 

 the hypoglossal nerve. It acts as an elevator of the hyoid bone or as a de- 

 pressor of the mandible. 



The Genio-glossus muscle arises just above the genio-hyoid, and it widens 

 out in a fan-shaped manner as its fibres pass backwards. The lowermost 

 fibres run downwards and backwards to the hyoid bone. In front they are 

 covered by the genio-hyoid, and behind they disappear under cover of the 

 hyo-glossus, but between these two muscles they lie in contact with the 

 mylo-hyoid. The uppermost fibres pass into the tongue, under cover of the 

 hyo-glossus. The genio-glossus receives its nerve-supply from the hypo- 

 glossal. The lower and middle fibres protrude the tongue (Fig. 50), while 

 the upper fibres retract it. When the muscle acts as a whole it depresses 

 the tongue. 



The Stylo-glossus runs downwards and forwards from the styloid process 

 to the side of the tongue, and in most of its extent it is covered by the 

 mandible. It helps the anterior fibres of the genio-glossus to retract the 

 tongue, and is supplied by the hypoglossal nerve. 



The Sublingual Salivary Gland lies immediately below the 

 mucous membrane of the anterior part of the floor of the mouth, 

 and it forms a small swelling, which can be readily appreciated 

 by the tip of the tongue. It lies on the surface of the anterior 

 part of the genio-glossus, and is placed under cover of the man- 

 dible. It possesses numerous ducts, which open directly into 

 the floor of the mouth. Occlusion of these ducts gives rise to a 

 cystic swelling (ranula), which is sometimes bilateral in the 

 floor of the mouth and lies under the tongue. 



The Lingual Nerve (p. 183) runs forwards on the upper part 

 of the hyo-glossus above the submaxillary duct, which passes 

 upwards under cover of it anteriorly. It disappears under 

 cover of the sublingual gland, and sinks into the genio-glossus 

 to reach the mucous membrane of the tongue. It supplies the 

 anterior two-thirds of the tongue with ordinary sensation and 

 with the special sense of taste, the latter through the fibres of 

 the chorda tympani, which joins the lingual nerve in the infra- 

 temporal fossa (pterygo-maxillary region). 



Development of the Neck. In the early weeks of fcetal life, 

 certain transverse ridges, which are known as the visceral or 

 branchial arches, appear on each side of the neck, and their 

 inner surfaces project into that part of the foregut (p. 287) 



