5C6 SPINAL NERVES. 



The external brandies supply the muscles at the side of the neck, viz., the 

 Cervicalis ascendens, Transversalis colli, and Trachelomastoid. 



The external branch of the second cervical nerve is the largest; it is often 

 joined with the third, and supplies the Complexus, Splenius, and Trachelo- 

 mastoid muscles. 



The internal branches, the larger, are distributed differently in the upper and 

 lower part of the neck. Those derived from the third, fourth, and fifth pier ves 

 pass between the Semi-spinalis and Complexus muscles, and, having reached the 

 spinous processes, perforate the aponeurosis of the Splenius and Trapezius, and 

 are continued outwards to the integument over the Trapezius ; whilst those derived 

 from the three lowest cervical nerves are the smallest, and are placed beneath the 

 Semi-spinalis, which they supply, and do not furnish any cutaneous filaments. 

 These internal branches supply the Complexus, Semi-spinalis colli, Inter-spinales, 

 and Multifidus spinee. 



The posterior branches of the three first cervical nerves require a separate 

 description. 



The posterior branches of the first cervical nerve (suboccipitaT) is larger than the 

 anterior, and escapes from the spinal canal between the occipital bone and the 

 posterior arch of the atlas, lying behind the vertebral artery, and enters the tri- 

 angular space formed by the Kectus posticus major, the Obliquus superior, and 

 Obliquus inferior. It supplies the Eecti and Obliqui muscles, and the Com- 

 plexus. From the branch which supplies the Inferior oblique a filament is given 

 off, which joins the second cervical nerve. It also occasionally gives off a cuta- 

 neous filament, which accompanies the occipital artery, and communicates with the 

 occipitalis major and minor nerves. 



The posterior division of the first cervical has no branch analogous to the 

 external branch of the other cervical nerves. 



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

 than the anterior branch, and the largest of all the other posterior cervical nerves. 

 It emerges from, the spinal canal between the posterior arch of the atlas and 

 lamina of the axis, below the Inferior oblique. It supplies this muscle, and 

 receives a communicating filament from the first cervical. It then divides into 

 an external and an internal branch. 



The internal branch, called, from its size and distribution, the occipitalis major, 

 ascends obliquely inwards between the Obliquus inferior and Complexus, and 

 pierces the latter muscle and the Trapezius near their attachments to the cranium. 

 It is now joined by a filament from the third cervical nerve, and, ascending on the 

 back part of the head with the occipital artery, divides into two branches, which 

 supply the integument of the scalp as far forwards as the vertex, communicating 

 with the occipitalis minor. It gives off an auricular branch to the back part of 

 the ear, and muscular branches to the Complexus. 



The posterior branch of the third cervical is smaller than the preceding, but 

 larger than the fourth ; it differs from the posterior branches of the other cervical 

 nerves in its supplying an additional filament to the integument of the occiput. 

 This occipital branch arises from, the internal or cutaneous branch beneath the 

 Trapezius ; it pierces that muscle, and supplies the skin on the lower and back 

 part of the head. It lies to the inner side of the occipitalis major, with which it 

 is connected. 



The internal branches of the posterior divisions of the first three cervical 

 nerves are occasionally joined beneath the Complexus by communicating branches. 

 This communication has been described by Cruveilhier as the posterior cervical 

 plexus. 



THE BEACHIAL PLEXUS (fig. 285). 



The brachial plexus is formed by the union of the anterior branches of the four 

 lower cervical and first dorsal nerves. It extends from the lower part of the side 

 of the neck to tne axilla, being very broad, and presenting but little of a plexi- 



