CERVICAL PLEXUS. 695 



neck and to the diaphragm ; and (c) communicating branches to the vagus, accessory, 

 hypoglossal, and sympathetic nerves. 



For convenience of description, the nerves derived from the plexus may be 

 classified as follows : 



I. Superficial (cutaneous) Branches 



A. Ascending Branches (C. 2, 3). B. Descending (supra-clavicular) Branches (C. 3, 4). 



N. occipitalis minor (lesser Nn. supraclaviculares anteriores (O.T. supra 



occipital), sternal), 



N. auricularis magnus (great Nn. supraclaviculares medii (O.T. supra-clavi- 



auricular), cular), 



N. cutaneus colli (O.T. trans- Nn. supraclaviculares posteriores (O.T. supra- 



verse superficial cervical). acromial). 



II. Deep (muscular and communicating) Branches 



A. Lateral Branches. B. Medial Branches. 



1. Muscular branches to 1. Muscular to 



Sterno-mastoid (C. 2), Pre vertebral muscles (C. 1, 2, 3, 4), 



Trapezius (C. 3, 4), Infra-hyoid muscles (C. 1, 2, 3) 



Levator scapulae (C. 3, 4), (ansa hypoglossi), 



Scaleni (medius and posterior) (C. 3, 4). Diaphragm (C. 3, 4, 5) (phrenic 



2. Communicating branches to nerve). 



Accessory nerve (C. 2, 3, 4). 2. Communicating branches to 



Vagus nerve (C. 1, 2), 

 Hypoglossal nerve (C. 1, 2), 

 Ansa hypoglossi (C. 2, 3), 

 Sympathetic (C. 1, 2, 3, 4). 



The second, third, and fourth cervical nerves are the chief nerves engaged in 

 forming the plexus. The first cervical nerve only enters into the formation of a 

 small part the medial portion of the deep part of the plexus. 



Superficial Cutaneous Branches. These nerves, six in number, are entirely 

 cutaneous. They radiate from the plexus, and appear in the posterior triangle of 

 the neck at the posterior border -of the sterno-mastoid muscle. They are divisible 

 into two series the one ascending: lesser occipital, great auricular, and nervus 

 cutaneus colli; the other descending (supra -clavicular): posterior, middle, and 

 anterior. 



Ascending Branches. The lesser occipital nerve is variable in size and is 

 sometimes double. Its origin is from the second and third cervical nerves (more 

 rarely from the second only). It extends backwards under cover of the sterno- 

 mastoid, and then upwards along its posterior border. Piercing the deep fascia near 

 the apex of the posterior triangle, it divides into auricular, mastoid, and occipital 

 branches, and supplies small cervical branches to the upper part of the neck. The 

 auricular branch supplies the skin of the cranial surface of the auricle ; the 

 mastoid and occipital branches supply the scalp. The nerve communicates on 

 the scalp with the greater occipital and great auricular nerves, and with the posterior 

 auricular branch of the facial nerve. 



The great auricular nerve is the largest of the cutaneous branches. It arises 

 from the second and third cervical nerves (or, more rarely, from the third alone). 

 Winding round the posterior border of the sterno-mastoid muscle, it courses 

 vertically upwards towards the ear. In this course it crosses the sterno-mastoid 

 muscle obliquely and is covered by the platysma muscle. Before arriving at the 

 ear it subdivides into mastoid, auricular, and facial branches. The mastoid branches 

 ascend over the mastoid process and supply the skin of the scalp behind the ear, 

 communicating with, the lesser occipital and posterior auricular nerves. The 

 auricular branches ascend to the ear and supply the lower part of the auricle on 

 both aspects ; they communicate with the same nerves. The facial branches, 

 passing over the angle of the mandible and through the substance of the parotid 



