RAT. 63 



known as the arbor mice,. Make a sketch of it. Cut 

 transversely through the rest of cerebellum and medulla, 

 and in the section see the folds of cerebellum cut in the 

 opposite direction, and, below, the thick floor of the 

 medulla. Cut through the medulla farther back. Do 

 you find a central canal in the section? 



On the ventral surface of the neck, just outside the caro- 

 tids, dissect away carefully, keeping the fore legs stretched 

 out, until you find nerves (white cords) going from the ver- 

 tebral region to the sides of neck. Can you make out two 

 roots to each nerve? Just in front of the ribs notice that 

 the nerves are larger, and that they go to the fore limb just 

 in front of subclavian artery and vein. How many of 

 these nerves as they arise from the neck interlace to form 

 the brachial plexus (the network from which the limb 

 nerves arise). Trace them into the limb. Sketch the 

 plexus. 



Separate the muscles in the bend of the knee, exposing 

 the large sciatic nerve. Trace the nerve backwards towards 

 the trunk. Does it pass through any bones? Trace the 

 nerve inside the dorsal wall of the body-cavity. Do you 

 find a plexus like that of the fore limb? If so, how many 

 nerves enter into its formation? 



