'////; CERVICAL PLEXl S <nr, 



spread i nit after tin' manner uf a fan, and, as they approach tho middle line, extend 

 iVdiii th(> chin to tlie st(>rnuni (lig. (177). The upper two or three of these twigs unite, 

 beneath the platysma, with the cervical (inframandibular) branch of the facial and 

 thus form loops, r'rom the terminal branches of the nerve numerous twigs arise 

 which pierce the platysma and end in the skin of the front part of the neck. 



The descending or supra-clavicular branches. These are derived from the 

 third and fourth cervical nerves (figs. (>7f> and (i7lii,and arise under cover of the sterno- 

 mastoid. At their commencements they are usually united with the muscular 

 branches destined for the trapezius. They become superficial at the middle of the 

 posterior border of the sterno-mastoid, and as they pass downwards they pierce the 

 deep cervical fascia. (1) The anterior supra-clavicular (suprasternal) branches 

 (fig. 677) are small, and cross over the clavicular origin of the sterno-mastoid to 

 reach the integument over the upper part of the manubrium sterni. They also 

 supply the sterno-chivicular joint. (2) The middle supra-clavicular (supra- 

 clavicular) nerves are of considerable size. They cross in front of the middle 

 third of the clavicle under cover of the platysma, and are distributed to the skin 

 covering the upper part of the pectoralis major as low as the third rib. (3) The 

 posterior supra-clavicular (supra-acromial) branches (fig. 677) cross the clavi- 

 cular insertion of the trapezius and the acromion process. They are distributed to 

 the skin which covers the upper two-thirds of the deltoid muscle and they supply 

 the aeromio-clavicular joint. 



DEEP BRANCHES OF THE CERVICAL PLEXUS 



The deep branches of the plexus pass outwards and dorsalwards, or ventralwards 

 and inwards; therefore they form two series, the external and the internal. 



The external branches of the deep series include communicating branches from 

 the second, third, and fourth cervical nerves to the spinal accessory nerve, and 

 muscular branches to the sterno-mastoid and the scalenus medius, levator scapulae, 

 and trapezius. 



The communicating branches of the external. The communicating branch 

 from the second cervical nerve is ultimately distributed to the sterno-mastoid, and 

 those from the third and fourth nerves end in the trapezius. 



1. The Nerve to the Sterno-mastoid arises from the second cervical nerve (fig. 

 677). 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 (fig. 676) are derived from the third 

 and fourth cervical nerves close to their exit from the intervertebral foramina. 



3. The Nerves to the Levator Scapulae (fig. 676) are derived from the third 

 and fourth cervical nerves, and occasionally from the second. They pierce the super- 

 ficial surface of the levator scapulae, and supply the upper three divisions of that 

 muscle. 



4. The branches to the Trapezius (fig. 676) are usually in the form of two stout 

 twigs which are given off by the third and fourth cervical nerves. They emerge from 

 under cover of the sterno-mastoid at its posterior border and cross the posterior 

 superior triangle of the neck at a lower level than the spinal accessory nerve (fig. 677). 

 They pass under cover of the trapezius in company with the last-named nerve, and 

 communicate with it to form the subtrapezial plexus, from which Ihe trapezius is 

 supplied. 



The internal branches of the deep series also comprise communicating and 

 muscular branches. 



The communicating branches of the internal (figs. 675 and 676) include 

 (1) branches which connect each of the first four cervical nerves with the superior 

 cervical ganglion of the sympathetic; (2) a communicating branch to the vagus; 

 (3) a communicating branch to the hypoglossal: and (4) communicating branches 

 which pass from the second and third cervical nerves to the descendens hypoglossi 

 (see p. <SS). The ultimate distribution of the twigs connected with the sympathetic 

 and the vagus nerves is not known, but the fibres which pass to the hypoglossal 

 nerve pass from it to the thyreo-hyoideus muscle, and to the descendens hypoglossi. 

 and the latter communicates with the branches from the second and third cervical 

 nerves, forming with them a loop, the ansa hypoglossi, which lies on the carotid 



