POSTERIOR DIVISIONS OF SPIXAL XERVES 779 



por^terior, 2»articularly in the case of the upper sacral nerves. The posterior primary 

 divisions are distrihuted to the intcfrunient of the occiput, posterior aspect of tlie 

 neck, of the back, and of the greater part of the gluteal region. They also supj)ly 

 the muscles of the posterior part of the neck and the muscles of the back, with the 

 exception of such of the posterior cervical and dorsal muscles as are connected with 

 the superior extremity, the serrati postici, and the levatores costarum. 



The anterior primary divisions may be broadly stated to supply the anterior 

 surface of the l>ody from the level of the chin downwards, and also the limbs. Each 

 anterior division is comiected with the sympathetic system by rami communi- 

 cantes. The anterior divisions contrast forcibly with the posterior divisions in the 

 great size that they attain to in the lower cervical and lumbo-sacral regions. In 

 these regions they communicate with one another to form plexuses, from which a 

 number of branches are given off to supply the limbs. 



POSTERIOR PRIMARY DIVISIONS 



The posterior primary divisions of the spinal nerves are, Avith the exception 

 of the first and second cervical nerves, smaller than the anterior divisions. With 

 the exception of the first cervical, the fourth and fifth sacral and the coccygeal 

 nerves, each nerve divides shortly after its commencement into an internal and an 

 external branch. 



CERVICAL NERVES. — The posterior divisions of the first and second cervical 

 reipiire separate description. The third, fourth, and fifth cervical ner\-es are of 

 small size. They pass backwards at the outer border of the semispinalis colli, 

 and divide into internal and external branches. 



The internal branches pass between the semispinalis colli and the complexus, 

 giving twigs to both these muscles and to the multifidus spinte. They then j)ass 

 between the complexus muscle and the ligamentum nuchae, pierce the origin of 

 the trapezius, and are distributed to the integument of the back of the neck. As 

 they enter the fascite they are directed ujnvards and outwards. The branch from 

 the third nerve is directed nearly vertically upwards, and is called the third or 

 smallest occipital nerve. It connnunicates with the great occipital nerve and 

 reaches the integument of the occiput. 



The external branches are distributed to the trachelo-mastoid, the cervicalis 

 ascendens, the transversalis colli, and to the splenius. 



The internal branches of the sixtii, seventh, and eighth cervical nerves pass 

 under cover (tf the semispinalis colli, and end in that muscle and in the adjacent 

 ))art of the multifidus spina\ The external branches are distributed to the com- 

 plexus, splenius, cervicalis ascendens, and transversalis colli muscles. 



The posterior primary division of the first cervical nerve passes backwards 

 between the posterior arch of the atlas and tlie vertel)ral artery, and traverses the 

 fatty tissue which occu})ies the triangular space bounded by the ol)liquus superior, 

 the oljlicpus inferior, and the rectus capitis posticus major. It gives? a branch to 

 each of these three muscles, and a twig which crosses the superficial surface of the 

 rectus capitis posticus major to reach the rectus capitis posticus minor. Another 

 twig forms a communicating loo]i with the great occipital nerve on the posterior 

 surface of the oWiquus inferior. A l)raneh is also furnished to the complexus. In 

 a few cases it gives a cutaneous twig to the back of the occiput. 



The posterior division of the second cervical nerve divides into a small 

 external and a very large internal ln-anch. The external branch gives a twig to the 

 obli(|UUs inferior, and ends in the complexus and trachelo-mastoid nuiscles. The 

 internal branch is the great occipital nerve. It gives ofif communicating l)ranches 

 which pass upwards and downwards, forming loops with the first and third cervical 

 nerves. In this manner a small plexus (i)osterior cervical plexus of Cruveilhier) 

 is formed. The great occipital nerve is then directed upwards, crossing the trian- 

 gular space descril)ed in connection with the first nerve, and being covered by the 

 complexus. It gives one or two twigs to the latti-r muscle, and then ])ierces it to 

 reach the deep surface of the trapezius. It pierces the outer border of the trape- 



