CERVICAL XERVES 7S5 



process, and are distributed to the skin which invests the upper two-thirds of the 

 deltoid muscle. They supply the acromio-clavicular joint. 



Deep Branches 



External branches. — The.se consist of communicating branches from the second 

 and third cervical nerves to the signal accessory, and of muscular branches which 

 supply the sterno-mastoid, scalenus medius, levator anguli scapulae, and trapezius. 



1. The nerve to the sterno-mastoid arises from the second cervical nerve. It 

 pierces the deep surface of the sterno-mastoid, and communicates within the muscle 

 with the spinal accessory nerve. 



2. The nerves to the scalenus medius are derived from the third and fourth 

 cervical nerves close to their exit from tli(! intervertebral foramina. 



3. The nerves to the levator anguli scapulae are derived from the third and 

 fourth nerves, and occasionally from the second. They pierce the superficial surface 

 of the levator anguli, and supply the upper three divisions of that muscle. 



4. The branches to the trapezius are usually in the form of two stout twigs 

 which are given off Ijy the third and fourth cervical nerves. They emerge at the 

 posterior border of the sterno-mastoid, and cross the posterior superior triangle oi 

 the neck at a lower level than the spinal accessory nerve. They pass under cover 

 of the trapezius in company with the last-named ners-e, and communicate with it 

 to form the subtrapezial plexus, from which the trapezius is supplied. 



Internal branches. — The internal set of deep branches comprise communicat- 

 ing branches and muscular branches. 1. The communicating branches pass to 

 the vagus and hypoglossal nen^es, from the loop formed by the first and second 

 nerves, and to the sympathetic from all of the four ner^^es which enter into the 

 cervical plexus. The muscular branches are distributed to the rectus capitis 

 lateralis, to the recti capitis antici major and minor, to the longus colli, to tlie 

 depressors of the hyoid bone (communicantes hypoglossi), and to the diaphragm 

 (phrenic nerve). 



2. The branch to the rectus capitis lateralis is furnished to that muscle l)y 

 the first nerve as it cro.^ses the deep surface of the muscle. 



3. The nerve to the rectus capitis anticus minor is given off by the first 

 nerve at the upper part of the loop in front of the transverse process of the atlas. 



4. The rectus capitis anticus major receives twigs from the upper four cervi- 

 cal nerv^es. 



5. The longus colli receives branches from the second, third, and fourth cervi- 

 cal nerves, and additional branches also from the fifth and sixth nerves. 



6. The communicantes hypoglossi are given off by the second and third 

 cervical nerves, and run oblicpiely downwards and inwards in front of the great 

 vessels of the neck to form a loop, the ansa hypoglossi, with the so-called descen- 

 dens hypoglossi. They supply the depressor muscles of the hyoid bone. (See 

 HvpoGLOss.\L Nerve. ) 



7. The PHRENIC NERVE may arise by one, two, or three roots, the strongest, 

 and occasionally the only, root being derived from the fourth cervical nerve. A 

 root from the fifth is commonly ])resent, and is usually associated either with the 

 nerve to the subclavius or Avith the communicating branch which passes from the 

 cervical to the brachial plexus. A slender root from the third nerve is occasionallv 

 present. The cervical sympathetic also furnishes a communicating twig. The 

 phrenic ner\'e passes downwards and inwards under cover of .the sterno-mastoid, 

 cros.sing obliquely in front of the scalenus anticus muscle. It is Crossed by the tran.s- 

 verse cervical and suprascapular arteries, and also by the omo-hyoid muscle. It 

 pa.sses behind the subclavian vein, and enters the thorax. In this situation it crosses 

 in front of or behind the commencement of the internal manmiarv artery, and is 

 commonly joined at this point by a communicating twig from the nerve to the sub- 

 clavius muscle. On the left side it is crossed, in addition, by the terminal part of 

 the thoracic duct. 



The further course of the phrenic differs on the two sides. On the right side 

 the nerve passes downwards, running on the outer side of the right innominate 

 vein, the superior vena cava, and the pericardium. Vietween these structures and 

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