THE INFRA-HYOID REGION. 75 



referred to; the hypoglossal enters the region superficial 

 to the external carotid and below the stylo-hyoid and 

 digastric muscles, and passes upwards over the cornu of 

 the hyoid bone between the glands and the hyo-glossus 

 muscles, covered in by the mylo-hyoid ; it loops with the 

 gustatory and is seen distributed to the extrinsic muscles 

 of the tongue. The gustatory nerve, with the chorda 

 tympani, lies beneath the gland and passes to the mucous 

 membrane of the sides and tip of the tongue, upon its 

 deeper portion. 



The above relations are those borne by the different 

 structures in this region, when the head is in its natural 

 position, but when the parts are the seat of operation, 

 the head is thrown back and the contents of the space 

 put on the stretch ; by so doing the position of the sub- 

 maxillary gland and the facial vessels are considerably 

 altered by the cavity which naturally exists between the 

 lower jaw and the mylo-hyoid muscle becoming flattened, 

 thereby causing a protrusion of the structures between 

 them. 



SURGICAL ANATOMY OF THE INFRA-HYOID 

 REGION. 



The boundaries of this region are, above, the hyoid 

 bone and the base of the tongue ; laterally, the sterno- 

 mastoid muscles (and carotid vessels) ; and below, the 

 upper border of the manubrium sterni, or interclavicu- 

 lar notch ; posteriorly, the cervical vertebrse, covered by 

 the longi colli muscles. This region is surgically im- 

 portant as containing the larynx and trachea, the cervi- 

 cal portion of oasophagus, and the thyroid body, with 

 their respective vessels and nerves. Its surface mark- 

 ings have been already described (vide Neck). 



