THE LATERAL VERTEBRAL REGION 



403 



is inserted by a broad attachment into the upper surface of the first rib, behind 

 the groove for the subclavian artery, as far back as the tubercle. It is separated 

 from the Scalenus anticus by the subclavian artery below and by the cervical 

 nerves above. The posterior 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 superficial surface, with the Sternomastoid ; it is crossed by the clavicle, 

 the Omohyoid muscle, subclavian artery, and cervical nerves. To its outer side is the Levator 

 anguli scapulae and the Scalenus posticus muscle. 



The Scalenus posticus (m. scalenus posterior), the smallest of the three Scaleni, 

 arises, by two or three separate tendons, from the posterior tubercles of the trans- 

 verse 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 Ser- 

 ratus magnus. This is the most deeply 

 placed of the three Scaleni, and is 

 occasionally blended with the Scalenus 

 medius. 



Nerves. The Scalenus anticus receives 

 branches from the fourth to the seventh 

 cervical; the Scalenus medius from the third 

 to the eighth cervical; and the Scalenus 

 posticus, from the fourth to the eighth cer- 

 vical nerves. 



Actions. 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 verte- 

 bral column to one or the other side. If the 

 muscles of both sides act, lateral movement 

 is prevented, but the vertebral column 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, are in- 

 vested by the deep cervical fascia, which 

 softens down their form, and is of consid- 

 erable importance in connection with deep 

 cervical abscesses and tumors, modifying 

 the direction of the growth of tumors and 

 of the enlargement of abscesses, and 

 causing them to extend laterally instead 



of toward the surface. The Platysma does not influence surface form except when 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 Sternomastoid is the most 

 important muscle of the neck as regards its surface form. If the muscle is put into action by 

 drawing the chin downward and to the opposite shoulder, its surface form will be plainly out- 

 lined. The sternal origin will stand out as a sharply defined ridge, while the clavicular origin 

 will present a flatter and not so prominent 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 visible, forming an oblique rounded ridge, terminating below 

 in a sharp outline of the sternal head. The posterior border of the muscle does not show above 

 the clavicular head. The anterior border is defined by drawing a line from the tip of the mas- 

 toid process to the sternoclavicular joint. It is an important surface-marking in the pperation 



FIG. 310. Scaleni muscles. (Poirier and Charpy.) 



