278 THE SPINAL NERVES. 



Direction. The first cervical nerve is directed horizontally outwards. The 

 roots of the lower cervical and dorsal nerves at first descend over the spinal cord, 

 held in contact with it by the arachnoid, till they arrive opposite the several 

 intervertebral foramina, where they are directed horizontally outwards. The nerves 

 of the cauda equina run in the direction of the spinal canal. 



Division of the nerves. The two roots of each of the spinal nerves unite 

 immediately beyond the ganglion, and the trunk thus formed separates, as already 

 mentioned, into two divisions, an anterior or ventral and a posterior or dorsal, 

 which are called primary branches or divisions, and each of which contains fibres 

 proceeding from both the anterior and posterior roots. 



Fig. 187. PLAN OP THE MODE OP BRANCHING OF A SPINAL NERVE. 



Before dividing in the manner above described each spinal nerve gives off a small 

 recurrent or meningeal branch, which is joined by a filament from the com- 

 municating cord between the anterior division of the nerve and the sympathetic, 

 and then runs inwards through the intervertebral foramen to the spinal canal, 

 where it is distributed to the vertebrae and ligaments, to the blood-vessels of the 

 canal, and to the dura mater (Luschka, Riidinger). 



POSTERIOR PRIMARY DIVISIONS OP THE SPINAL NERVES. 



The posterior divisions of the spinal nerves are, with few exceptions, smaller 

 than those given to the fore part of the body. Springing from the trunk which 

 results from the union of the roots of the nerve in the intervertebral foramen, or 

 frequently by separate fasciculi from the two roots, each turns backwards at once, 

 and soon divides into two parts, distinguished as external and internal, distributed 

 to the muscles and the integument behind the spine. The first cervical, the fourth 

 and fifth sacral, and the coccygeal are the only nerves the posterior divisions of 

 which do not separate into external and internal branches. 



SUBOCCIPITAL NERVE. The posterior division of the first cervical or suboccipital 

 nerve, slightly larger than the anterior, emerges over the arch of the atlas, between 

 this and the vertebral artery, and enters the space bounded by the larger rectus 

 and the two oblique muscles, where it divides into branches for the surrounding 

 muscles. 



(a) One branch descends to the inferior oblique, and gives a filament, through 

 or over the fibres of that muscle, to join the second cervical nerve. 



() Another ascends over the rectus posticus major muscle, supplying it and the 

 smaller rectus. 



(c) A third enters the superior oblique muscle. 



(d) A fourth sinks into the complexus, where that muscle covers the nerve and 

 its branches. 



Variety. A cutaneous branch is occasionally given to the back of the head : it accompanies 

 the occipital artery, and is connected beneath the integument with the great and small occipital 

 nerves. 



