SCALENI MUSCLES. 75 



The outer part of the subclavian artery having been already prepared, 

 let the dissector remove more completely the fibrous tissue from the nerves 

 of the brachial plexus. From the plexus trace the small branch to the 

 subclavius muscle ; and the branches to the rhomboid and serratus muscles, 

 which pierce the middle scalenus. If it is thought necessary, the anterior 

 scalenus may be cut through after the artery has been studied. 



Clean the cervical plexus, and seek its muscular branches, the small 

 twigs to join the descendens noni, and the roots of the phrenic nerve. 

 Lastly, let the middle scalenus muscle be defined, as it lies beneath the 

 cervical nerves. 



The SCALENI muscles are usually described as three in number, and are 

 named from their relative position, anterior, middle, and posterior ; they 

 extend from the first two ribs to the transverse processes of the cervical 

 vertebra. 



The SCALENUS ANTICUS (fig. 16, l ) extends from the first rib to the 

 lower cervical vertebras, and is somewhat conical in shape. 'It is attached 

 by its apex to the inner border and the upper surface on the first rib, so as 

 to surround the rough surface or projection on this aspect of the bone ; and 

 by its base it is inserted into the anterior transverse processes of four of 

 the cervical vertebra, viz., sixth, fifth, fourth, and third (fig. 45, c ). 



More deeply seated below than above, the muscle is concealed by the 

 clavicle and the subclavius, and by the clavicular part of the sterno-mas- 

 toid : the phrenic nerve lies along its cutaneous surface, and the subclavian 

 vein crosses over it near the rib. Along the inner border is the internal 

 jugular vein. Beneath the scalenus are the pleura, the subclavian artery, 

 and the nerves of the brachial plexus. The insertion into the vertebrae 

 corresponds with the origin of the rectus capitus anticus major muscle. 



Action. The anterior of these muscles raises strongly the first rib, in 

 consequence of its forward attachment. If the rib. is fixed, it bends for- 

 ward the lower part of the neck. 



The SCALENIUS MEDIUS MUSCLE (fig. 16, 2 ) is larger than the anterior, 

 and extends farthest of all on the vertebras. Inferiorly it is attached to a 

 groove on the upper surface of the first rib, extending obliquely forwards 

 from the tubercle to the outer border for one inch and a half. The muscle 

 ascends behind the spinal nerves, and is inserted into the tips of the poste- 

 rior transverse processes of all the cervical vertebrae (fig. 45, D ). 



In contact with the anterior surface are the subclavian artery and the 

 spinal nerves, together with the sterno-mastoid muscle ; whilst the poste- 

 rior surface touches the posterior scalenus, and the deep lateral muscles of 

 the back of the neck. The outer border is perforated by the nerves of the 

 rhomboid and serratus muscles. 



Action. Usually it elevates the first rib. With the rib fixed, the cer- 

 vical part of the spine will be inclined laterally by one muscle. 



The SCALENUS POSTICUS (fig. 45, p ) is considerable in size, and appears 

 to be but part of the preceding. It is attached below by a slip, about half 

 an inch wide, to the second rib, in front of the serratus posticus superior; 

 and it is inserted above with the scalenus medius into two or three of the 

 lower cervical transverse processes. 



Action. It acts as an elevator of the second rib ; and its fibres having 

 the same direction as those of the medius, it will incline the neck in the 

 same way. 



The SUBCLAVIAN ARTERY (fig. 16) is the first part of the large vessel 

 supplying the upper limb with blood, which is thus designated from its 



