THE CERVICAL PLEXUS. 287 



nerves, turns forwards over the sterno-mastoid muscle about the middle, and after 

 perforating the cervical fascia, divides beneath the platysma myoides into two 

 branches, which are distributed to the anterior part of the neck. 



(a) The upper branch is the larger, and gives an ascending twig which accom- 

 panies the external jugular vein, and communicates freely with the cervical branch 

 of the facial nerve ; it is then transmitted through the platysma to the surface, 

 and ramifies in the integument of the upper half of the front of the neck, filaments 

 reaching as high as the lower maxilla. 



(b) The lower branch, sometimes represented by two or three smaller offsets, 

 likewise pierces the platysma and is distributed below the preceding, its filaments 

 extending in front as low as the sternum. 



Varieties. The superficial cervical nerve also may arise from the third only, or from the 

 third and fourth cervical nerves. It is sometimes represented by two or more branches arising 

 separately from the plexus. 



SUPERFICIAL DESCENDING BRANCHES. 



Supraclavicular nerves. The descending series of the superficial nerves are 

 thus named. They arise together from the third and fourth cervical nerves, and 

 descend in the interval between the sterno-mastoid and the trapezius muscles. As 

 they approach the clavicle, they are three or more in number, and are recognized 

 as internal, middle, and external. 



(a) The internal branch (suprasternal), which is much smaller than the rest, 

 ramifies over and below the inner third of the clavicle, and terminates near the 

 sternum. From it one or two filaments are furnished to the sterno-clavicular 

 articulation (Riidinger, Hepburn). 



(b) The middle branch, generally divided into two or three parts, and crossing 

 the clavicle in the interval between the sterno-nlastoidand trapezius muscles, distributes 

 some twigs over the fore part of the deltoid, and others over the pectoral muscle as 

 low as the third rib. The latter join the small anterior cutaneous branches of 

 some of the upper intercostal nerves. 



(c) The external or posterior branch (supra-acromial) is directed outwards across 

 the clavicular attachment of the trapezius muscle, and ramifies over the acromion 

 and in the integument of the outer and back part of the shoulder. 



Filaments from these nerves supply the skin over the lower part of the posterior 

 triangular space, and one or two twigs pass backwards over the trapezius to the 

 integument above the spine of the scapula. 



Variety. One of the middle branches of the supraclavicular nerves occasionally perforates 

 the clavicle on its way downwards. 



DEEP BRANCHES : INTERNAL SERIES. 



Connecting branches. The cervical plexus is connected near the base of the 

 skull with the pneumo-gastric, hypoglossal, and sympathetic nerves, by means of 

 filaments intervening between those nerves and the loop formed by the first two 

 cervical nerves in front of the atlas (p. 283). 



Muscular branches. Branches to the pre vertebral muscles proceed from the 

 cervical nerves close to the vertebrae, including the loop between the first two of 

 these nerves ; and from the fourth nerve a twig is frequently given to the upper 

 part of the scalenus anticus. 



Two communicating cervical branches, one from the second, the other 

 from the third cervical nerve, descend over or under the internal jugular vein to 

 join the descending cervical nerve in the ansa cervicalis, from which the infrahyoid 

 muscles are supplied (p. 273). 



T 2 



