BRACHIAL PLEXUS. 459 



posteriorly to that vessel, and emerges into the triangular space formed 

 by the rectus posticus major, obliquus superior, and obliquus inferior. 

 It is distributed to the recti and obliqui muscles, and sends one or two 

 filaments downwards to communicate with the second cervical nerve. 

 The posterior branch of the second cervical nerve is three or four times 

 greater than the anterior branch, and is larger than the other posterior 

 cervical nerves. The posterior branch of the third cervical nerve is 

 smaller than the preceding, but larger than the fourth ; and the other 

 posterior cervical nerves go on progressively decreasing to the seventh. 

 The posterior branches of the fourth, fifth, sixth, seventh, and eighth 

 nerves pass inwards between the muscles of the back in the cervical 

 and upper part of the dorsal region, and reaching the surface near the 

 middle line, are reflected outwards, to be distributed to the integu- 

 ment. The fourth and fifth are nearly transverse in their course, and 

 lie between the semispinalis colli and complexus. The sixth, seventh, 

 and eighth are directed nearly vertically downwards ; they pierce the 

 aponeurosis of origin of the splenius and trapezius. 



POSTERIOR CERVICAL PLEXUS. This plexus is constituted by the 

 succession of anastomosing loops and communications which pass be- 

 tween the posterior branches of the first, second, and third cervical 

 nerves. It is situated between the complexus and semispinalis colli, 

 and its branches are the 



Musculo-cutaneous, 

 Occipitalis major. 



The Musculo-cutaneous branches pass inwards between the com- 

 plexus and semispinalis colli to the ligamentum nuchae, distributing 

 muscular filaments in their course. They then pierce the aponeurosis 

 of the trapezius and become subcutaneous, sending branches outwards 

 to supply the integument of the posterior aspect of the neck, and up- 

 wards to the posterior region of the scalp. 



The Occipitalis major is the direct continuation of the second cer- 

 vical nerve ; it ascends obliquely inwards, between the obliquus in- 

 ferior and complexus, pierces the complexus and trapezius after pass- 

 ing for a short distance between them, and ascends upon the posterior 

 aspect of the head between the integument and occipito-frontalis, in 

 company with the occipital artery. The Occipitalis major sends 

 numerous branches to the muscles of the neck, and is distributed to 

 the integument of the scalp, as far forwards as the middle of the 

 vertex of the head. Its branches communicate with those of the 

 Occipitalis minor. 



BRACHIAL PLEXUS. 



The Brachial or axillary plexus of nerves is formed by communica- 

 tions between the anterior branches of the four last cervical and first 

 dorsal nerve. These nerves are all similar in size, and their mode of 



