SCALENE MUSCLES 323 



the brachial plexus and the subclavian artery. It arises from 

 the anterior tubercles of the transverse processes of the third, 

 fourth, fifth, and sixth cervical vertebrae, and, tapering some- 

 what as it descends, it is inserted into the scalene tubercle 

 on the inner margin of the first rib, and also into the 

 superior surface of the same bone between the two subclavian 

 grooves. 



The upper part of its anterior surface is concealed by the 

 sterno-mastoid and the lower part by the clavicle. The 

 common carotid artery descends along its medial border. 

 Between it and the sterno-mastoid lie the internal jugular 

 vein ; the intermediate tendon of the omo-hyoid ; the phrenic 

 nerve, passing downwards and medially; and the transverse 

 cervical and transverse scapular arteries passing postero- 

 laterally, superficial to the phrenic nerve. Between it and 

 the clavicle lies the subclavian vein. 



Its posterior surface is in relation, above, with the tips of 

 the lower cervical transverse processes, and below, with the 

 apex of the pleura, the second part of the subclavian artery, 

 and its costo-cervical branch. The lateral border touches the 

 roots of the brachial plexus, and the medial border is in 

 relation with the thyreo-cervical artery, its inferior thyreoid 

 branch, and with the vertebral artery. 



Musculus Scalenus Medius. This is a more powerful 

 muscle than the preceding. It springs from the posterior 

 tubercles of all the cervical transverse processes (with the 

 exception, in some cases, of the first), and it is inserted into 

 a rough oval impression which marks the upper surface of 

 the first rib between the tubercle of the rib and the groove 

 for the subclavian artery. 



It forms part of the floor of the posterior triangle of the 

 neck. Its superficial surface is in relation with the brachial 

 plexus and the third part of the subclavian artery. Its 

 posterior border touches the levator scapulae ; and the dorsal 

 scapular nerve and the descending branch of the transverse 

 cervical artery pass between it and that muscle. The lower 

 part of its anterior border is in relation with the apex of 

 the pleura, and the upper two roots of the long thoracic 

 nerve pierce the substance of the muscle. 



Musculus Scalenus Posterior. The scalenus posterior is 

 generally inseparable, at its origin, from the scalenus medius. 

 It is the smallest of the three, and springs by two or three 



ii 21 a 



