752 



SPINAL NERVES. 



are situated somewhat in a line with the 

 angles of the ribs, so that they become more 

 external in proportion to their inferior posi- 

 tion. 



The posterior branches of the lumbar nerves 

 are analogous in their distribution to the four 

 lower dorsal branches, having an external 

 large musculo-cutaneous, and small internal 

 muscular divisions. The external branches 

 run along the deep surface of the longissimus 

 dorsi, and at its outer edge perforate the 

 tendon of the latissimus dorsi, and terminate 

 in cutaneous filaments directed over the crest 

 of the ileum to the glutaeal region, as far as 

 on a level with the great trochanter. The 

 internal branches are lost in the substance of 

 the multifidus spinae. 



The posterior branches of the sacral nerves 

 exist as distinct branches within the spinal 

 canal, and consequently differ from the cer- 

 vical, dorsal, and lumbar, which become dis- 

 tinct trunks after the main trunks have issued 

 from the spinal or intervertebral foramina. 

 They decrease in size from above downwards, 

 being extremely small, and passing out of the 

 posterior sacral foramina, the fifth coming 

 out between the sacrum and coccyx. They 

 form a minute anastomosis with each other, 

 and with the corresponding branch of the 

 last lumbar, and after having given filaments 

 to the lower part of the erector spinse, per- 

 forate the tendon of that muscle, and are 

 distributed to the skin over the sacrum and 

 coccyx, and immediately around the anus. 



The anterior branches of the spinal nerves 

 are much larger than the posterior branches, 

 the two upper cervical forming the only ex- 

 ception. They form intricate plexuses in the 

 neck, the lower part of the spine and sacrum, 

 the nerves given off from those in the first 

 situation being principally intended for the 

 neck and upper extremities ; in the two last 

 for the lower extremities. The intervening 

 series represented by the thoracic nerves, being 

 comparatively simple in their distribution, do 

 not form plexuses. 



The Anterior Branches of the Cervical Nerves. 



The anterior branch of the first cervical 

 nerve, smaller than the posterior, is di- 

 rected between the occipital bone and the 

 transverse process of the atlas, passes over 

 the outer edge of the vertebral artery, and 

 appears at the inner side of the rectus ca- 

 pitis lateralis. It then descends, and forms an 

 anastomotic arch with the anterior branch of 

 the second, in front of the transverse process. 

 In its course the rectus capitis lateralis, and 

 rectus capitis anticus minor receive one or 

 more filaments, and it also sends a filament 

 into the canal for the vertebral artery, and 

 which communicates with the trunk of the 

 second cervical between the transverse pro- 

 cesses of the atlas and axis. From this ana- 

 stomotic arch are given off filaments which 

 communicate with the lingual and par vagum 

 and superior cervical ganglion of the sym- 

 pathetic. 



The anterior branch of the second cervical 



nerve, also much smaller than the posterior 

 passes forwards between the transverse pro- 

 cesses of the atlas and the axis, being con- 

 cealed by the levator anguli scapulas, splenius, 

 and first inter-transverse muscle, and divides 

 into an ascending branch, passing in front of 

 the transverse process of the atlas, to com- 

 municate with the first cervical j and a de- 

 scending branch. 



The descending branch soon subdivides, 

 and gives several filaments of communication 

 with the superior cervical ganglion ; one small 

 filament to communicate with the par vagum, 

 another enters the rectus capitis anticus 

 major, and the last concurs to form the cer- 

 vical plexus. 



Anterior branch of the third cervical nerve, 

 larger than the posterior, and twice as large 

 as the preceding, passes between the verte- 

 bral artery and inter-transverse muscles, and 

 having given branches to the levator anguli 

 scapula? and rectus capitis anticus major, com- 

 municates above with the descending branch 

 of the second, below with that of the fourth, 

 and in the interval with the superior cervical 

 ganglion, and then again bifurcates to enter 

 into the formation of the cervical plexus. 



The anterior branch of the fourth cervical 

 nerve, of the same size as the preceding, 

 communicates above with the third, below 

 with the fifth cervical, in the middle with the 

 superior cervical ganglion, and then enters 

 into the formation of the lower part of the 

 cervical plexus. 



The cervical plexus (the deep cervical plexus) 

 is composed of the primary and secondary 

 anastomosing arches of the anterior branches 

 of the four upper cervical nerves. These 

 anastomosing arches are subject to consider- 

 able variation, though generally formed by 

 each nerve bifurcating, and, after having com- 

 municated with the nerve above and -below, 

 again reuniting in a more or less uniform 

 manner prior j to giving off their terminal 

 branches. The plexus is situated deeply at 

 the upper anterior and outer part of the neck 

 behind the posterior edge of the sterno-mastoid, 

 in front of the scalenus posticus, external to 

 the rectus capitis anticus major, the carotid 

 artery, jugular vein, and par vagum. It con- 

 stitutes the chief contents of the posterior 

 superior cervical triangle, and is surrounded 

 by a large quantity of loose cellular membrane, 

 absorbent glands, and fat, and immediately in- 

 vested with a prolongation of the deep cervical 

 fascia, which renders the dissection of the nu- 

 merous branches as they immediately proceed 

 from it, difficult. It communicates internally 

 by several delicate filaments with the superior 

 and middle cervical ganglia of the sympathetic; 

 below with the upper part of the brachial 

 plexus, and externally with the spinal acces- 

 sory, giving several filaments to the muscles 

 with which it is in immediate relation. The 

 branches given off from the cervical plexus 

 may be divided as follows, into 



[ Superficialis colli. 



Superficial ascending | Aurictilaris magnus. 

 lOccipitalis minor. 



