THE NECK. 147 



nerve, and below it, sometimes a vein. The artery lies under the muscle, while the 

 veins may be either on or under the muscle or both. 



The apex of the angle formed by the tendon of the digastric muscle is held 

 down to the hyoid bone by a slip of fascia which is an expansion of the central 

 tendon of the muscle and the tendon of the stylohyoid muscle. The distance at 

 which the central tendon of the digastric is held away from the hyoid bone varies 

 in different individuals and is an important fact to bear in mind in searching for 

 the artery. If the tendon rests high above the hyoid bone the artery must be 

 looked for low down, sometimes even under the tendon; if, on the contrary, the 

 tendon is low down the artery may be o. 5 to i cm. higher up. The hypoglossal nerve 

 lies on the muscle and nearer to the mandible than the artery. If there is a vein on 

 the hyoglossus muscle it is apt to be below the nerve, that is, nearer the hyoid bone, 

 and may lie directly over the artery. The vein and the nerve are to be displaced 

 up towards the jaw and an incision a centimetre long made through the hyoglossus 

 muscle a short distance above the digastric tendon and parallel with the hyoid bone. 

 This incision should not be deep, as the muscle is only 2 or 3 mm. ( y% in. ) thick. 



Middle scalene muscle 



Posterior scalene muscle 



Steraomastoid muscle, , . , ___ _ , _ 



.-^ / / I } \ \ ^--Omohyoid muscle 



Phrenic nerve 



Anterior scalene muscle ^ / I I 



Subclavian vein / / \ Suprascapular artery and vein 



Cords of brachial plexus / Transverse cervical artery and vein 



Subclavian artery 



FIG. 175. Ligation of the Subclavian artery 



The edges of the incision being raised and displaced upward and downward, the artery 

 will probably be seen running at right angles to the fibres of the muscle and parallel to 

 the hyoid bone. If not seen at once it should be looked for below the incision, 

 nearer to the hyoid bone. Care must be taken not to mistake the vein for the artery. 

 That this is not an unlikely thing is shown by its occurring in the hands of a distin- 

 guished surgeon who had had exceptional experience in this same operation. The 

 ligature needle may be passed from above downward to avoid including the hypo- 

 glossal nerve. 



Subclavian Artery. The right subclavian artery runs from the sternoclavicular 

 articulation in a curved line to the middle of the clavicle. It rises 1.25 cm. (^ in., 

 Walsham) above the clavicle. The innominate bifurcates opposite the right sterno- 

 clavicular joint. The left subclavian springs directly from the arch of the aorta, 

 therefore it is longer than the right by 4 to 5 cm. , this being the length of J)he in- 

 nominate. As the subclavian artery passes outward it is crossed by the scalenus 

 anticus muscle, which divides it into three parts : the first part, extending to the 

 inner side of the muscle, gives off three branches, the vertebral, internal -mammary, 

 and thyroid axis; the second part, behind the muscle, gives off the superior intercos- 

 tal; the third part has no branches. 



