THE CERVICAL MUSCLES. 547 



into the upper surface of the first rib, behind the groove for the subclavian artery. 

 Some fibres of the muscle may extend across the first intercostal space to be inserted 

 into the outer surface of the second rib. 



Nerve-Supply. — By branches from the anterior divisions of the cervical 

 nerves. 



Action. — To bend the neck laterally, or, if the cervical vertebrae be fixed, to 

 raise the first rib, assisting in inspiration. 



Relations. — As the middle scalene passes downward to its insertion it diverges 

 from the scalenus anterior, so that a triangular interval exists between the two 

 muscles through which the subclavian artery and the brachial plexus pass, these 

 structure^ lying in front of the insertion of the scalenus medius. 



3. Scalenus Posticus (Fig. 542). 



Attachments. — The posterior scalene (m. scalenus posterior) lies immediately 

 behind the scalenus medius and anterior to the ilio-costalis cervicis. It arises by 

 two or three tendinous slips from the transverse processes of the lower two or three 

 cervical vertebrae and passes downward and laterally to be inserted into the outer 

 surface of the second rib. 



Nerve-Supply. — From the anterior divisions of the lower three cervical 

 nerves. 



Action. — To bend the neck laterally, or, if the cervical vertebrae be fixed, to 

 raise the second rib. 



Variations of the Scalene Muscles. — There is not a little variation in the extent of the 

 upper attachments of the scalene muscles, the origins being increased or, more usually, dimin- 

 ished in number. A certain amount of fusion may also occur, especially between the medius 

 and posterior, so that it is not always possible to distinguish these two muscles. Occasionally 

 the subclavian artery perforates the lower portion of the anterior scalene, and the portion so 

 separated may form a distinct muscle, the scalenus iiiiuimus, which lies in the interval, bet ween 

 the anterior and middle scalenus, and is attached above to the transverse processes of the sixth 

 or the sixth and seventh cervical vertebrae and below to the upper surface of the first rib and to 

 the dome of the pleura. 



A muscle occasionally occurs between the upper part of the pectoralis major and the 

 upper external intercostals, from both of which it is separated by a lamella of areolar tissue. 

 It is termed the sitpracostalis, and takes its origin from the first rib and sometimes also from the 

 fascia which covers the anterior scalene, and passes downward to be inserted into the outer 

 surface of the third and fourth ribs, sometimes attaching also to the second rib and sometimes 

 descending as low as the fifth. It has been regarded as an aberrant portion of the pectoralis 

 major or rectus abdominis, but it seems to be more probably a portion of the obliquus muscu- 

 lature and is apparently related to the scaleni. 



4. Rectus Capitis Lateralis. 



Attachments. — The rectus capitis lateralis is a short, flat muscle which arises 

 from the transverse process of the atlas and is inserted into the inferior surface of 

 the jugular process of the occipital bone. 



Nerve-Supply. — From the suboccipital nerve. 



Action. — To bend the head laterally. 



5. Intertransversales Anteriores. 



Attachments. — The anterior intertransversales are a series of small muscles 

 which pass between the anterior tubercles of the transverse processes of the cervical 

 vertebrae. 



Nerve-Supply. — From the anterior divisions of the cervical nerves. 



Action. — To bend the head laterally. 



The Triangles of the Neck. — The sterno-cleido-mastoid muscle, on account 

 of its position somewhat superficial to the remaining muscles of the neck, serves to 

 divide that region into two triangular areas which are of considerable importance 

 from the stand-point of topographic anatomy. 



