978 THE NERVOUS SYSTEM 



anastomose with twigs of the posterior auricular, great auricular, and great occipital nerves 

 (fig. 753). 



(2) The great auricular nerve arises from the second and third cervical nerves 

 (figs. 751, 752). It accompanies the small occipital to the posterior border of 

 the sterno-mastoid, but at that point it diverges from the small occipital (fig. 753) 

 and runs upward and forward across the sterno-mastoid toward the angle of the 

 mandible. When it is about half-way across the muscle it begins to break up into 

 its terminal branches, which are named, according to the area of their distribution, 

 mastoid, auricular, and facial. 



As the nerve ascends obliquely across the sterno-mastoid it is embedded in the deep cervical 

 fascia, is covered by superficial fascia and the platysma, and it hes parallel with and shghtly 

 dorsal to the external jugular vein, (a) The mastoid branch is small, and is distributed to the 

 integument covering the mastoid process. It anastomoses with the posterior auricular and small 

 occipital nerves. (6) The auricular branches are three or four stout twigs which interlace with 

 the branches of the posterior auricular nerve; they cross the superficial surface of the posterior 

 auricular branch of the facial, and are distributed to the skin on the back of the auricle with the 

 exception of its uppermost part. One or two twigs pass through fissures in the cartilage of the 

 auricle, and are distributed to the integument on the lateral surface of the lobule and the lateral 

 surface of the lower part of the hehx and anthelix. (c) The facial branches pass upward and 

 forward among the superficial lobules of the parotid gland, and supply the skin over that gland 

 and immediately in front of it, and they anastomose in the substance of the gland with the cer- 

 vico-facial division of the facial nerve. In some cases fine twigs may be traced forward nearly 

 to the angle of the mouth. 



Transverse branch of the plexus. — The superficial cervical cutaneous nerve 



(transverse cervical) arises from the second and third cervical nerves (figs. 751, 

 752), and appears at the posterior border of the sterno-mastoid, a little below the 

 great auricular nerve. It passes transversely across the sterno-mastoid under 

 cover of the integument, platysma, and external jugular vein, and divides into a 

 number of twigs which spread out after the manner of a fan, and, as they approach 

 the middle fine, extend from the chin to the sternum (fig. 753). 



The upper two or three of these twigs unite, beneath the platysma, with the cervical (infra- 

 mandibular) branch of the facial and thus form loops. From 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. 751, 752), and arise under cover of the 

 sterno-mastoid. At their commencements they are usually united with the mus- 

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

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

 pierce the deep cervical fascia. They include the following: 



(1) The anterior supra-clavicular (suprasternal) branches (fig. 753) are small, and cross 

 over the clavicular attachment of the sterno-mastoid to reach the integument over the upper part 

 of the manubrium sterni. They also supply the sterno-clavicular 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 cover- 

 ing the upper part of the pectorahs major as low as the third rib. (3) The posterior supra- 

 clavicular (supra-acromial) branches (fig. 753) cross the clavicular 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 acromio-clavicular joint. 



Deep Branches of the Cervical Plexus 



The deep branches of the plexus pass lateralward and dorsalward, or ventral- 

 ward and medial ward; therefore they form two series, the lateral and the medial. 



The lateral branches of the deep s(>ries 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 scap- 

 ulae, and trapezius. 



The communicating branches. — The communicating branch from the second cervical 

 nerve is ulliniutcly di.stributcd 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. 753). 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. 752) are derived from the third or fourth 

 to the eighth cervical nerves close to their exit from tlic intervertebral foramina. 



