ANTERIOR ASPECT OF HEAD AND NECK. 



The acromial run through or over the Trapezius insertion, and 

 over the clavicle externally, to supply the shoulder down to 

 the lower third of the Deltoid. [617-619] 



Deep Branches (muscular and communicating). External 

 series. These run toward the posterior triangle as follows: To 

 (C. 2) the deep surface of the Sterno-mastoid, communicating 

 under it with the spinal accessory. To (C. 3 and 4) the Trape- 

 zius, communicating under it, and in the posterior triangle, 

 with the spinal accessory. To (C. 3 and 4) the Scaleni, medius 

 and posticus, and outer surface of the Levator anguli scapulae. 

 Internal series. These run toward the anterior triangle as fol- 

 lows : To (C. 1 to 4) the sympathetic superior cervical ganglion. 

 To (loop between C. 1 and 2) all the Recti, the vagus (incon- 

 stant), and the hypoglossal; the latter branch sends a menin- 

 geal branch upward on the hypoglossal and then, probably, 

 entirely constitutes its descendens hypoglossi branch and its 

 branches to the Thyro-hyoid, Genio-hyoid, and (possibly) in- 

 trinsic muscles of the tongue. To (C. 2, 3, and 4) the Inter- 

 trans versales, Longus colli, and Rectus capitis anticus major. 

 To (C. 4) the upper part of the Scalenus medius. The descend- 

 ing cervical (C. 2 and 3) are two long branches which join in 

 front of the internal jugular and form a loop (ansa hypoglossi) 

 with the descendens hypoglossi in front of the carotid 

 sheath; branches of the loop supply the Omo-hyoid, Ster- 

 no- thyroid, and Sterno-hyoid; the latter branch may con- 

 tinue behind the sternum to join the cardiac plexus, or the 

 phrenic. [619] 



Phrenic. This is derived mainly from the fourth cervical 

 and partly from the third (either directly or through the nerve 

 to the Sterno-hyoid) and the fifth (either directly or through 

 the nerve to the Subclavius) ; it often communicates with the 

 cervical sympathetic system. Its roots unite, descend upon 

 the Scalenus anticus, and pass between the subclavian vessels 

 on their way to the diaphragm. [621] 



Brachial Plexus. This is formed by the anterior primary 



[67] 



