REPORT ON THE SPHENISCID^. 159 



with the skin, they supply. The anterior divisions of the last two cervical nerves pass 

 backwards, and unite with the first dorsal to form the single cord which in the Penguins 

 represents the brachial plexus. 



The Brachial Plexus. 



The brachial plexus (fig. l) is formed by the union of the anterior branches of the last 

 two cervical and first dorsal ^ nerves, and receives a communicating twig from the second 

 dorsal nerve.^ These nerves pass out from the intervertebral foramina lying between 

 the scalenus muscle above and the lateral muscles of the root of the neck below. They 

 unite together to form a single cord, which escapes from the thorax along with the 

 subclavian artery by passing over the second rib to reach the axilla. As it passes from 

 the thorax, the single cord lies between the sujara- and infra-spinatus muscles above, 

 and the pectoralis minor below, and between these muscles it breaks up into branches for 

 the supply of the wing. 



Previously to its union with the other nerves which form the single cord of the 

 brachial plexus, the second last cervical nerve gives oif certain branches. They are 

 arranged as follows : — 



(a) The nerve to the rhomboid, trapezius, and levator scapuloB (1)^ winds upwards 

 between the shoulder girdle and the wall of the chest, to reach the deeper surface of the 

 rhomboid muscle, where it divides into three branches, which are distributed to the three 

 muscles above named. 



{h) The nerve to the pectoralis medius (2) passes downwards through the foramen 

 situated on the inner side of the upper extremity of the coracoid bone, and enters the 

 deeper surface of the muscle which it supplies. A subordinate twig is given off from this 

 nerve to supply the eoraco-brachialis. 



From the single large cord which represents the brachial plexus, the following branches 

 are derived: — 



(a) The nerve to the pectoralis major (3), which passes downwards, and enters the 

 deeper surface of that muscle. From this nerve a subordinate branch is supplied to the 

 " muscle des parures," and another to the pectoralis minor. 



(6) The nerve to the serratus anticus major and serratus anticus minor (4). This 

 nerve arises from the plexus, above the origin of the nerve to the pectoralis major. It 

 pierces the serratus anticus minor, and after giving off" branches to that muscle, termi- 

 nates in the serratus anticus major. 



^ By first dorsal nerve I mean that nerve wliicli lies in tlie intercostal space which is bounded in front by the first 

 or rudimental rib, and behind by the second rib. The designation of this nerve is dependent on the view held regarding 

 the nature of the first or rudimental rib. By some anatomists it is considered to be the moveably articulated transverse 

 process of the last cervical vertebra, while by others it is regarded as the costal element of the first dorsal vertebra. I 

 liave adopted the latter view, and consequently enumerate the nerve in question among those of the dorsal region. 



^ The communicating branch from the second dorsal nerve is absent in Eadiiptes chrysolophus and in S^jheniscus 

 mcndiculus. 



^ The figures in brackets refer to the annexed diagram of the plexus. 



