THE CERVICAL NERVES. 1281 



the fourth and fifth sacral and the coccygeal nerve failing in this respect. Down to 

 and including the sixth thoracic nerve, the internal branches are mainly cutaneous and 

 the external entirely muscular. From the seventh thoracic down, the reverse con- 

 dition exists. In the former region the internal branches become cutaneous near the 

 spine, whilst in the latter the sensory filaments pass laterally for some distance through 

 the muscles before reaching their cutaneous distribution. 



THE CERVICAL NERVES. 



The first cervical nerve (n. suboccipitalis), the first of the spinal secies, is 

 atypical in several respects. Its posterior root is either insignificant or entirely absent, 

 and its posterior division, which does not divide into internal and external branches, is 

 larger than the anterior and usually does not send off any direct cutaneous branch. 

 The nerve passes dorsally between the occipital bone and the posterior arch of the 

 atlas and traverses the suboccipital triangle, occupying a position below and posterior 

 to the vertebral artery. Superficial to it is the complexus muscle. 



Branches. These are : (i) the muscular, (2) the communicating and (3) the 

 cutaneous. 



1. The muscular branches supply the superior and inferior oblique, the corn- 

 plexus and the rectus capitis posticus major and minor muscles. 



2. The communicating branch forms a loop with the second cervical nerve. It 

 usually arises in common with the twig to the inferior oblique muscle, through 

 or over which muscle it passes to reach its destination. It may arise with the 

 nerve to the complexus, after piercing which muscle it communicates with the great 

 occipital nerve. 



In the neck and close to the vertebrae is a series of loops between the posterior 

 divisions of the first, second, third and sometimes the fourth cervical nerves. This is 

 called fae posterior cervical plexus and from it filaments are distributed to the neigh- 

 boring muscles. 



3. The cutaneous branch is not always present. It accompanies the occipital 

 artery, inosculates with the small and great occipital nerves and supplies the occipital 

 region. 



The second cervical nerve is distinguished by the size of its posterior division, 

 (r. posterior) which is larger than the anterior (r. anterior). Its posterior division 

 takes a dorsal course between the atlas and the axis, and then between the inferior 

 oblique and semispinalis colli muscles. Reaching the deep surface of the complexus 

 it breaks up into its external portion (r. lateralis), which supplies the complexus, 

 obliquus inferior, semispinalis colli and multifidus spinse muscles, and its internal 

 portion (r. medialis). The latter is called the great occipital nerve (n. occipitalis 

 major). This nerve (Fig. 1087) passes upward over the inferior oblique, pierces 

 the complexus and trapezius, and accompanies the occipital artery to the scalp, 

 to the posterior half of which it is the main sensory nerve. It becomes superficial 

 at the superior nuchal line, at a point from 2-3 cm. lateral to the external' oc- 

 cipital protuberance, and spreads out into numerous branches which supply the 

 scalp as far forward as the vertex. 



The great occipital nerve communicates with the small and least occipital and the posterior 

 and great auricular nerves. 



Variations. An approximate balance is maintained between the great and small occipital 

 nerves, any deficiency in the distribution of either usually being equalized by a compensatory 

 enlargement of the other. Sometimes the great occipital sends a branch to the auricle. The 

 external branch may give off a cutaneous filament or may furnish a twig to the superior oblique. 



The third cervical nerve has a smaller posterior division than has the second. 

 Passing backward, the former helps to form the posterior cervical plexus and divides 

 into external and internal branches. The external branch (r. lateralis) supplies 

 adjacent muscles and the internal branch (r. medialis), known as the least or third 

 occipital nerve (n. occipitalis tertius), pierces the complexus, splenius and trapezius to 

 supply the skin of the occipital and posterior cervical regions (Fig. 1083). 



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