FEOQ 251 



III. Tlie peripheral nervous system. 



With the experience which he has now had in 

 dissecting muscles and in tracing blood-vessels, 

 the student ought to be able to trace the follow- 

 ing nerves, and to distinguish their more striking 

 features ; consequently only the names, origin, and 

 termination of the parts of the peripheral nervous 

 system will be given. 



a. The spinal nerves. 



Examine a spinal cord and note the connection 

 of each of the spinal nerves to the spinal cord by 

 means of an anterior or ventral and a posterior 

 or dorsal root. In which direction do these 

 roots run ? Is there any difference in this re- 

 spect between the roots of the anterior and those 

 of the posterior nerves? Trace the roots to the 

 intervertebral foramina. Do the roots unite in- 

 side the spinal canal? Turn the frog over on 

 its back, and note the nerves lying as white cords 

 on each side of the vertebral column. At their 

 point of issue from the spinal column they are 

 covered by a yellowish - white deposit of lime 

 secreted by the perigangUonic glands. This 

 may be neatly removed by gently teasing with 

 the point of a fine, sharp scalpel the pigmented 

 membrane which covers the limy patches, then 

 with a pipette carefully placing on each patch a 

 drop of dilute nitric or hydrochloric acid. The 

 acid dissolves the lime without injuring the sur- 

 rounding tissues. 



Under the patch may be found the point of 

 union of the two roots. Towards the cord from 

 this point look on the posterior root for the gan- 



