THE LATERAL VERTEBRAL REGION. 335 



tubercle on the inner border and upper surface of the first rib. The lower part 

 of this muscle separates the subclavian artery and vein, the latter being in front, 

 and the former, with the brachial plexus, behind. 



Relations. In front, with the clavicle, the Subclavius, Sterno-mastoid, and 

 Omo-hyoid muscles, the transversalis colli, the suprascapular and ascending cer- 

 vical arteries, the subclavian vein, and the phrenic nerve ; by its posterior surface, 

 with the Scalenus medius, pleura, the subclavian artery, and brachial plexus of 

 nerves. It is separated from the Longus colli, on the inner side, by the vertebral 

 artery. On the anterior tubercles of the transverse processes of the cervical ver- 

 tebrae, between the attachments of the Scalenus anticus and Longus colli, lies the 

 ascending cervical branch of the inferior thyroid artery. 



The Scalenus medius, the largest and longest of the three Scaleni, arises from 

 the posterior tubercles of the transverse processes of the lower six cervical vertebrae, 

 and, descending along the side of the vertebral column, is inserted by a broad 

 attachment into the upper surface of the first rib, behind the groove for the sub- 

 clavian artery, as far back as the tubercle. It is separated from the Scalenus 

 anticus by a subclavian artery below and the cervical nerves above. The pos- 

 terior thoracic, or nerve of Bell, is formed in the substance of the Scalenus medius 

 and emerges from it. The nerve to the Rhomboids also pierces it. 



Relations. By its anterior surface, with the Sterno-mastoid ; it is crossed by 

 the clavicle, the Omo-hyoid muscle, subclavian artery, and the cervical nerves. To 

 its outer side is the Levator anguli scapulae and the Scalenus posticus muscle. 



The Scalenus posticus, the smallest of the three Scaleni, arises, by two or three 

 separate tendons, from the posterior tubercles of the transverse processes of the 

 lower two or three cervical vertebrae, and, diminishing as it descends, is inserted 

 by a thin tendon into the outer surface of the second rib, behind the attachment of 

 the Serratus magnus. This is the most deeply placed of the three Scaleni, and is 

 occasionally blended with the Scalenus medius. 



Nerves. The Rectus capitis anticus major and minor and the Rectus lateralis 

 are supplied by the first cervical nerve, and from the loop formed between it and 

 the second ; the Longus colli and Scaleni, by branches from the anterior divisions 

 of the lower cervical nerves (fifth, sixth, seventh, and eighth) before they -form the 

 brachial plexus. The Scalenus medius also receives a filament from the deep 

 external branches of the cervical plexus. 



Actions. The Rectus anticus major and minor are the direct antagonists of the 

 muscles at the back of the neck, serving to restore the head to its natural position 

 after it has been drawn backward. These muscles also serve to flex the head, and, 

 from their obliquity, rotate it, so as to turn the face to one or the other side. The 

 Longus colli flexes and slightly rotates the cervical portion of the spine. The 

 Scaleni muscles, when they take their fixed point from above, elevate the first and 

 second ribs, and are, therefore, inspiratory muscles. When they take their fixed 

 point from below, they bend the spinal column to one or the other side. If the 

 muscles of both sides act, lateral movement is prevented, but the spine is slightly 

 flexed. The Rectus lateralis, acting on one side, bends the head laterally. 



Surface Form. The muscles in the neck, with the exception of the Platysma myoides, are 

 invested by the deep cervical fascia, which softens down their form, and is of considerable 

 importance in connection with deep cervical abscesses and tumors, modifying the direction of 

 their growth and causing them to extend laterally instead of toward the surface. The Platysma 

 myoides does not influence surface form except it is in action, when it produces wrinkling of the 

 skin of the neck, which is thrown into oblique ridges parallel with the fasciculi of the muscle. 

 Sometimes this contraction takes place suddenly and repeatedly as a sort of spasmodic twitching, 

 the result of a nervous habit. The Sterno-cleido-mastoid is the most important muscle of the 

 neck as regards its surface form. If the muscle is put into action by drawing the chin down- 

 ward and to the opposite shoulder, its surface form will be plainly outlined. The sternal origin 

 will stand out as a sharply-defined ridge, while the clavicular origin will present a flatter and not 

 so prominent an outline. The fleshy middle portion will appear as an oblique roll or elevation, 

 with a thick rounded anterior border gradually becoming less marked above. On the opposite 

 side i. e. on the side to which the head is turned the outline is lost, its place being occupied 

 by an oblique groove in the integument. When the muscle is at rest its anterior border is still 



