APPENDIX. CHAPTER XIX. 299 



does not interfere with the breathing muscles; but their action will 

 be almost at once so changed as to produce a sneeze, tending to clear 

 and protect the nose. 



2. Kill a frog with ether (note, p. 68); open its abdomen and re- 

 move the viscera. At the back of the abdominal cavity will be seen 

 a bundle of white cords (nerve-trunks) passing back to each leg. 

 They soon unite into one main stem (the sciatic nerve), which may 

 be easily dissected along its course until it ends in fine branches in 

 the hind limb. 



3. Kill a frog and expose the origin of the sciatic nerve as above. 

 With stout scissors then cut away bit by bit, and very carefully, the 

 bodies of the vertebrae (which will be seen projecting in the middle 

 line at the back of the abdominal cavity) until the neural canal is 

 laid open and the spinal cord exposed. You will probably fail the 

 first time, but on the second attempt succeed in doing this without 

 cutting the nerve trunks as they pass between the vertebrae to join 

 the spinal cord. On the specimen thus prepared the origin of the 

 nerves from the spinal cord, and their division into anterior and pos- 

 terior (ventral and dorsal) roots before they join the cord can be 

 demonstrated, also the ganglionic enlargements on the posterior 

 roots. 



4. The general form, the cervical and lumbar enlargements, etc., 

 of the spinal cord may be shown on a frog. Having killed the ani- 

 mal, remove the skin and muscles on the dorsal side of the spinal 

 column. With great care cut away the upper two thirds of the 

 neural arches of the vertebrae. Then remove the upper half of the 

 skull cavity. Gently raising piece by piece the exposed brain and 

 spinal cord, divide the nerves which spring from them and lift out 

 the whole cerebro-spinal centre and place it in alcohol for twenty- 

 four hours. Demonstrate the origin of nerves from both brain and 

 cord, the union of the brain and cord, etc. etc. The specimen may 

 be preserved in alcohol for future use. 



5. A frog's brain differs in many important points from that of 

 man, as in the very small cerebellum, the comparatively small cere- 

 bral hemispheres, the comparatively large mid-brain and the ab- 

 sence of convolutions. To demonstrate the main anatomical fea- 

 tures of the brain that of a mammal is necessary. 



a. Obtain a fresh calf's or sheep's head from a butcher. Dissect 

 away the skin and muscles covering the cranium. Then with a 

 small saw very carefully divide the bones in a circular direction, 

 so as to cut off those of the crown of the head. Next carefully 

 remove the loosened bones of the top of the skull, tearing them away 



