DEEP CERVICAL NERVES.- BRACIIIAL PLEXUS. 641 



The nerve of the left side is a little longer than that of the right, in conse- 

 quence of the oblique position of the pericardium round which it winds, 

 and also because of the diaphragm beiug lower on this than on the opposite 

 side. This nerve crosses in front of the arch of the aorta and the pul- 

 monary artery before reaching the pericardium. 



Besides the terminal branches supplied to the diaphragm, each phrenic nerve gives 

 filaments to the pleura and pericardium ; and receives sometimes an offset from the 

 union of the descendens noni with the cervical nerves. Swan notices this union as 

 occurring only on the left side. Luschka describes twigs from the lower part of the 

 nerve to the peritoneum, the inferior cava, and the right auricle of the heart. 



One or two filaments of the nerve of the right side join in a small ganglion with 

 branches to the diaphragm which are derived from the solar plexus of the sympa- 

 thetic ; and from the ganglion twigs are given to the suprarenal capsule, the hepatic 

 plexus, and the lower vena cava. On the left side there is a junction between the 

 phrenic and the sympathetic nerves near the oesophageal and aortic openings in the 

 diaphragm, but without the appearance of a ganglion. 



IV. DEEP BRANCHES : EXTERNAL SERIES. 



Muscular branches. The sterno-mastoid receives a branch from the 

 second cervical nerve. Two branches proceed from the third nerve to the 

 levator anguli scapulas ; and from the third and fourth cervical nerves, as 

 they leave the spinal canal, branches are given to the middle scalenus 

 muscle. Further, the trapezius has branches prolonged to it ; and thus, 

 like the sterno-mastoid, this muscle receives nerves from both the spinal 

 accessory and the cervical plexus. 



Connection with the spinal accessory nerve. In the substance of the sterno- 

 mastoid muscle, this nerve is connected with the branches of the cervical 

 plexus furnished to that muscle. It is also connected with the* branches 

 distributed to the trapezius the union between the nerves being beneath 

 the muscle, and having the appearance of a plexus ; and with another 

 branch of the cervical plexus in the interval between the two muscles. 



Summary of the cervical plexus. From the cervical plexus are distributed 

 cutaneous nerves to the ba?k of the head, to part of the ear and face, to the 

 anterior half of the neck, and to the upper part of the trunk. The muscles 

 supplied with nerves from the plexus are the sterno-mastoid, the platysma, 

 and the lower hyoid muscles in part ; the anterior recti, the levator anguli 

 scapulse, the trapezius, the scalenus medius, and the diaphragm. By means 

 of its branches the plexus communicates with the pneumo-gastric, spinal 

 accessory, hypoglossal, and sympathetic nerves. 



BRACHIAL PLEXUS. 



This large plexus, from which the nerves of the upper limb are supplied, 

 is formed by the union of the anterior trunks of the four lower cervical and 

 first dorsal nerves ; and it further receives a fasciculus from the lowest of 

 the nerves (fourth), which goes to form the cervical plexus. The plexus 

 extends from the lower part of the neck to the axillary space, and termi- 

 nates opposite the coracoid process of the scapula in large nerves for the 

 supply of the limb. 



The manner in which the nerves are disposed in the plexus is liable to 

 some variation, but the following may be regarded as the arrangement most 

 frequently met with. The fifth and sixth cervical are joined at the outer 

 border of the scalenus, and a little farther out receive the seventh nerve, 



