Nervous System. 541 



cord between each two of the vertebrae constituting the backbone. They 

 are, in man, commonly reckoned as thirty in number ; viz. , eight pairs 

 of cervical, twelve pairs of dorsal, five of lumbar and five sacral. Oc- 

 casionally there are six sacral, when the whole number becomes thirty- 

 one. Each pair of these nerves is in part motor and in part sensory. 

 But the only sense of which they are the vehicle is the sense of touch, 

 including that of pressure and heat, and they are often called the 

 nerves of general sensibility. The motor part of the cervical nerves 



FIG. 264. A portion of the spinal cord from the cervical region, showing connections of 

 the spinal nerves. 



A. Front view. B. Right side. (7. Cross-section. 



D. Underside of nerve-roots, and ganglion of posterior root. References same in all. 

 1. The anterior median fissure. 

 2. " posterior 



3. Antero-lateral impression place of Connection of anterior roots, (shown too dis- 

 4. Postero-lateral groove connection of posterior, afferent roots. [tinctly in fig.) 



5. Anterior, efferent roots. 

 5'. Anterior root divided and turned up (A). 

 6. Posterior root, the fibres of which enter 6'. 



6 .Ganglion of posterior root. 

 7. The united or compound nerve. 



7 .The posterior primary hrarich, made up of fibres from both the anterior and pos- 

 terior roots. (After Allen Thompson.) 



reach the muscles of the neck and occiput, upper part of the chest and 

 shoulder, "arm and fingers ; and a branch goes to the diaphragm ; while 

 the sensory portion of these nerves come from the skin of the neck, 

 shoulders, arms, ears, &c. The motor portion of the first, second and 

 third pairs of the dorsal nerves, mingle with the cervical in branches to 

 the muscles of the arms and shoulders. The other pairs reach themus- 



