(Continuation of the text of Fig. 54.) 



in our figure, the nerves appear thicker outside than inside the dorsal sac. As 

 tlie spinal cord ends at the ist or 2nd Lumbar V^ertebra, the course of the spinal 

 Nerves inside the canal becomes longer the lower their origin. Thus the first 

 Cervical Nerve runs horizontally outwards, the course of the next nerve is more 

 oblique etc; the lowest nerves run almost vertically downwards, parallel to the 

 Filum Terminale. They form with this last mentioned structure and the Conus 

 Terminalis, the so-called Cauda Equina. Injury below the second Lumbar Vertebra, 

 therefore, onl}' invohes the Cauda Equina, not the spinal cord. 



The spinal nerves arise by 2 roots, anterior and posterior ; these roots leave 

 the cord as root-fibres. As a rule, the posterior roots are thicker than the 

 anterior; an exception is, however, found in the ist Cervical Nerve — as shewn 

 in our figure — . Its posterior root-fibres are \ery slender; they may even 

 be absent. 



On every posterior root is a spinal ganglion, which lies in the interverte- 

 bral foramen; the posterior and anterior roots join outside. Just above the ist 

 Cervical Nerve our figure shews the Vertebral Artery leaving tlie foramen in the 

 transverse process of the Atlas and running horizontallv inwards. It then pierces 

 the Dura Mater and enters the cranial cavity. The Dura Mater does not extend 

 further down in the Spinal Canal than to the level of the 2nd Sacral Vertebra 

 in the adult, and to the 3rd Sacral Vertebra in the child (cf. figure). It ends in 

 a blind sac (cf. Fig. 55). These levels are of great importance, because injur}- or 

 operation above will necessarih' open the dural sac and ma}- be followed by 

 purulent Meningitis which in usually fatal. Below there is no danger of Meningitis. 

 This fact is taken advantage of in operations (Kraske's) in which portions of 

 the Sacrum are removed, in order to expose pelvic organs. Of course, when 

 removing portions of this bone, temporarily or permanently, one has to consider 

 the important nerves which should not be damaged. The Coccygeal Nerve which 

 emerges between the ist and 2nd piece of the Coccyx forms with a branch of 

 the 5th Sacral Nerve the Cocc}-geal Plexus which innervates the Skin over the 

 Coccyx. The 4th and 5th Sacral Nerves enter into the formation of the Sacral 

 Plexus, the former supplying the Levator Ani and Cocc\'geus Muscles is more 

 important than the latter. Damage to the Sacral Plexus means damage to the ■ 

 floor of the Pelvis. Twigs from it also go to the Bladder and Rectum. The 

 higher up one goes, the more important are the nerves for the innervation of 

 the pelvic muscles, pehic organs, and lower limbs (Great Sciatic Nerve). 



