142 The Pr&vertebral 



artery, and between its insertion and the origin of the rectus anticus 

 major is the ascending cervical artery. 



The scaienus medius, the largest of the scaleni, arises from the 

 upper surface of the first rib behind the groove for the subclavian 

 artery, and at once begins to be inserted into the posterior tubercles 

 of the transverse processes, beginning at the seventh and mounting 

 to the axis. 



Relations. It lies behind the scaienus anticus, from which it is 

 separated below by the subclavian artery and the dome of the pleura, 

 and above by the cervical nerves. Behind it are the scaienus posticus 

 and the levator anguli scapulae. The nerve of Bell (p. 251), which is 

 formed in the muscle, emerges from its outer surface. 



The scaienus posticus arises from the outer surface of the second 

 rib, and, ascending a little way behind the last muscle, is inserted into 

 the posterior tubercles of the two lowest cervical transverse pro- 

 cesses. 



The scalene muscles incline the head and neck downwards and to 

 the side, or, acting from above, help in inspiration. They are supplied 

 by the anterior divisions of the lower cervical nerves. 



The rectus capitis anticus major arises from the same points of bone 

 as those into which the scaienus anticus is inserted ; it is attached 

 above to the basilar process of the occiput. It is supplied by the upper 

 cervical nerves. In front of it are the pharynx, the sheath of the 

 internal carotid with its contents, and the sympathetic cord. 



Appreciation. The upper surface of the transverse processes of the 

 cervical vertebras are grooved for the comfortable transmission of the 

 cervical nerves ; the borders of the grooves end externally in the 

 anterior and posterior tubercles. The scaienus anticus is attached to 

 the anterior tubercles, and the middle and posterior scaleni are attached 

 to the posterior tubercles : therefore the cervical nerves emerge behind 

 the anterior scaienus, and in front of the other scaleni. 



The origin of the anterior scalene is between two grooves upon the 

 first rib, and, as, according to the rule, the veins above the dia- 

 phragm lie in a plane anterior to the arteries, the subclavian vein is in 

 front of, and the artery behind, the origin of the muscle. The phrenic 

 nerve arises from the third, fourth, and fifth cervical nerves, that is, upon 

 the outer side of the scaienus anticus, and it must pass inwards to enter 

 the thorax, and this it does in front of the muscle ; and, as the second 

 part of the subclavian artery is behind the scaienus anticus, and the nerve 

 descends upon the inner border of the muscle, it passes in front of the 

 first part of the artery, but, to make its course as short as possible, 

 behind the vein. 



The thyroid axis is given off in the first part of the subclavian 

 artery, and its supra- and posterior scapular branches must needs pass 

 outwards to their destination they run in front of the anterior scalene 

 and the phrenic nerve. 



