THE CERVICAL AND BRACHIAL PLEXUSES. 289 



branches are given to the middle scalenus muscle. Farther, the trapezius receives 

 one or more considerable branches which arise from the third and fourth cervical 

 trunks in common with the supraclavicular nerves. 



Communications with the spinal accessory nerve. In the substance of 

 the sterno-mastoid muscle, this nerve is connected with the branch 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 cutaneous 

 nerves are distributed to the side of the head, to part of the ear and face, to the 

 anterior two-thirds or more of the neck, and to the upper part of the chest and 

 shoulder. The muscles supplied with nerves from the plexus are the sterno-mastoid, 

 the trapezius, and the int'rahyoid muscles, the anterior and lateral recti capitis, the 

 longuscolli, the levator anguli scapulae, the scalenus medius and anticus in part, 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 the 

 greater part of the first dorsal nerves. It also receives in many cases a fasciculus 

 from the lowest of the nerves (fourth) which go to form the cervical plexus, or a 

 filament from the second dorsal nerve : these two roots may co-exist. The plexus 

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

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

 limb. 



The cervical or supraclavicular portion of the plexus, emerging from the cleft 

 between the scalenus anticus and medius, lies in the lower part of the posterior 

 triangular space, above and behind the third part of the subclavian artery : it is 

 crossed by the posterior belly of the omo-hyoid muscle, and is often pierced by the 

 transverse cervical or posterior scapular artery. After passing behind the clavicle, 

 the axillary or infraclavicular portion of the plexus is placed to the acromial side of 

 the axillary vessels, being enclosed in the axillary sheath, and covered by the 

 pectoralis major and subclavius muscles ; and at its termination it lies between the 

 pectoralis minor and subscapularis muscles. 



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

 variation, but the following may be regarded as the typical arrangement, from which 

 the different forms met with may in most cases be readily derived. The fifth and 

 sixth cervical join together at the outer border of the scalenus medius to form an 

 upper trunk ; similarly the eighth cervical and first dorsal unite together between 

 the scaleni muscles to form a lower trunk ; while the seventh cervical remains single, 

 forming a middle trunk. 



Soon after passing the outer border of the scaleni muscles, each primary trunk 

 divides into an anterior and a posterior branch. The posterior branch of the lower 

 trunk, however, is much smaller than the others, and in most instances is derived 

 solely from the eighth cervical nerve. The anterior branches of the upper and 

 middle trunks unite together to form what is called the upper or outer cord of the 

 plexus ; the large anterior branch of the lower trunk forms by itself the lower or 

 inner cord of the plexus ; and the posterior branches of all three trunks unite 

 together to form the middle or posterior cord. The cords thus formed lie at first in 

 a single bundle on the outer side of the first part of the axillary artery, but lower 



