BRANCHES BELOW THE CLAVICLE 639 



The muscular branches supply the Longus Colli, Scaleni, Rhomboidei, and 

 Subclavius muscles. Those for the Scaleni and Longus Colli arise from the 

 lower cervical nerves at their exit from the intervertebral foramina. The 

 rhomboid branch arises from the fifth cervical, pierces the Scalenus Medius, 

 and passes beneath the Levator Anguli Scapulae, which it occasionally supplies, 

 to the Rhomboid muscles. The nerve to the Subclavius is a small filament, 

 Which arises from the trunk formed by the junction of the fifth and sixth 

 cervical nerves ; it descends in front of the subclavian artery to the Subclavius 

 muscle, and is usually connected by a filament with the phrenic nerve. 



The posterior thoracic nerve (long thoracic, external respiratory of Bell), (Fig. 

 352) supplies the Serratus Magnus, and is remarkable for the length of its 

 course. It arises by two roots, from the fifth and sixth cervical nerves, imme- 

 diately after their exit from the intervertebral foramina. These unite in the 

 substance of the Middle Scalenus muscle, and, after emerging from it, the nerve 

 passes down behind the brachial plexus and the axillary vessels, resting on the 

 outer surface of the Serratus Magnus. It extends along the side of the chest 

 to the lower border of that muscle, and supplies it with numerous filaments. 



The suprascapular nerve (Fig. 353) arises from the cord formed by the fifth, 

 sixth, and seventh cervical nerves; passing obliquely outwards beneath the 

 Trapezius, it enters the supraspinous fossa, through the notch in the upper 

 border of the scapula; and, passing beneath the Supraspinatus muscle, curves 

 in front of the spine of the scapula to the infraspinous fossa. In the supra- 

 spinous fossa, it gives off two branches to the Supraspinatus muscle, and an 

 articular filament to the shoulder-joint ; and in the infraspinous fossa, it gives 

 off two branches to the Infraspinatus muscle, besides some filaments to the 

 shoulder-joint and scapula. 



BRANCHES BELOW THE CLAVICLE. 



Anterior thoracic 

 Subscapular. 

 Circumflex. 

 Musculo-cutaneous. 

 Internal cutaneous. 



To arm, forearm, and hand \ ^, es , s . er internal cutaneou s. 



] Median. 



Ulnar. 

 [_ Musculo-spiral. 



The branches given off below the clavicle, are derived from the three cords 

 of the brachial plexus, in the following manner. 



From the outer cord, arises the external of the two anterior thoracic nerves, 

 the musculo-cutaneous nerve, and the outer head of the median. 



From the inner cord, arises the internal of the two anterior thoracic nerves, 

 the internal cutaneous, the lesser internal cutaneous (nerve of Wrisberg), the 

 ulnar and inner head of the median. 



From the posterior cord, arise the three subscapular nerves ; and the cord then 

 divides into the musculo-spiral and circumflex nerves. 



The Anterior Thoracic Nerves (Fig. 352), two in number, supply the Pectoral 

 muscles. 



The external, or superficial branch, the larger of the two, arises from the outer 

 cord of the brachial plexus, passes inwards, across the axillary artery and vein; 

 and is distributed to the under surface of the Pectoralis Major. It sends down 

 a communicating filament to join the internal branch. 



The internal, or deep branch, arises from the inner cord, and passes upwards 

 between the axillary artery and vein (sometimes perforates the vein), and joins 

 with the filament from the superficial branch. From the loop thus formed, 

 branches are distributed to the under surface of the Pectoralis Minor and 

 Pectoralis Major muscles. 



