406 SPECIAL ANATOMY. 



b. Ram. posterior is small, is distributed in the m. multifid., 

 compkxus, gives other branches, and terminates in the m. 

 splenius capitis, or upon the skin. 



Plexus cervicalis, formed by the loops of the four superior cer- 

 vical nerves (their anterior branches), is situated behind m. sterno- 

 cleidom. and ven. jugular is interna, before the superior extremity 

 of m. scalenus med. and levat. scapula, the third and fourth cervi- 

 cal vertebrae. Its branches have been described. 



655. b. The four inferior cervical nerves 



supply more especially the skin and muscles of the superior extre- 

 mity, as their strong anterior branches interlace, upon their exit 

 from the intervertebral foramina, and form, with the first dorsal 

 nerve, the plexus brachialis. The posterior branches are small, 

 incline round m. multifidus, &c., supply splenius, biventer, &c., 

 and terminate upon the skin of the middle line, at the inferior re- 

 gion of the neck. 



656. Plexus brachialis. 



Situation : oblique from the inferior lateral region of the neck as 

 far as the inner side of the head of the humerus. Its superior 

 broader portion lying between the mm. scaleni, covered by a fascia, 

 is situated above art. subclavia in the trigonum cervicale inferius, 

 and is connected above with plex. cervicalis and n. phrenicus. Its 

 central narrower portion between clavicle and first rib, behind art. 

 axillaris. Its inferior portion in the axilla, behind the m. pectoralis 

 major, before the scapula-humeral articulation, separated from this 

 by the tendons of the m. subscapularis, surrounds the art. axillaris. 

 The branches are spirally interwoven. 



657. a. Respiratory nerves, the branches of the 



pars supra-clavicular is. 



1. N. dorsalis scapula, arises from the ram. anter. of the fifth 

 cervical vertebra, descends obliquely backwards through the m. 

 scalen. medius, above levator. scap., and with art. dorsalis sca- 

 pula on the internal surface of mm. rhomboidei ; distributes mus- 

 cular branches. 



2. N. thorac'icus longus (posterior) s. respiratorius externus 

 Bellii, arises with three roots, from the fifth to seventh cervical 

 nerves, which perforate the scalenus medius. Its trunk descends 

 on the external surface of serratus antic, major as far as its infe- 

 rior extremity, before m. scapularis ; its branches pass in arches 

 into the Serratus Magnus. 



