278 DETAILED SYNTHESIS. 



tissue, called the ganglion of the posterior or sensatory 

 root of the nerve. On all the sensatory nerves or sensa- 

 tory parts of nerves extending from the cranium, a sim- 

 ilar ganglion is found. Hence, these ganglia are thought 

 essential to sensation, but in what manner is not known : 

 some of the nerves terminate in them. 



678. THE USES OP THE SPINAL CORD are twofold: 

 1st, it is a large bundle of nerves, connecting the Brain 

 and various other parts of the body ; and 2d, it is a chain 

 of nervous centres, causing action in the various parts 

 with which it has connection. 



679. Illus. IF THE SPINAL CORD OF A FROG IS CUT ABOVE HIS HIPS, 



and his hind-foot is pricked, it will be immediately moved , but no pain 

 is caused, since he makes no effort to remove his body, as he will do if 

 his fore-foot is pricked. Accidents have injured the spinal cord hi cases 

 where, if a feather was drawn across the sole of the foot, motion would 

 be caused ; yet it was not by the will of the patient, for he felt neither 

 the feather nor the motion. The feather through the nerves affected the 

 centres hi the cord, and they sent down an influence that caused the 

 muscles to contract. 



Sympathetic Ganglia. 



680. THE SYMPATHETIC GANGLIA DIFFER FROM THE 

 CRANIO-SPINAL in these respects : tKe latter are protected 

 within a bony case, while the former aje not ; they are 

 very numerous, but all very small, while some of those 

 of the Cranium are very massive. 



681. THE SYMPATHETIC GANGLIA, , WITH THEIE 

 NERVES, FORM a double chain on each side of the spinal 

 column, extending, in fact, from the head to the extrem- 

 ity of the coxcyx. Several are found in the head, three 

 in each side of the neck, and one near each exit of the 

 nerves from the remaining length of the spinal column. 



682. THE SYMPATHETIC GANGLIA CONNECT with 

 each other, and with the spinal and cranial nerves ; they 



678. What are ? 679. Describe the effect . 680. How do ? 681. What 

 do ? 682. With what ? 



