46 LABORATORY OUTLINE OF NEUROLOGY 



40. Here review the dissection of the fish brain and deter- 

 mine the precise limits of its chief subdivisions in comparison 

 with those of the embryonic human brain. Note particularly 

 the relative size of the cerebral hemispheres in the brains of 

 various animals and that certain other parts of the brain tend 

 to vary with the size of the cerebral cortex (thalamus, pons, 

 cerebellar hemispheres, etc.). These parts are known as 

 cortical dependencies. It should be borne in mind that these 

 gross subdivisions are not functionally independent, but are 

 connected by long tracts of fibers. 



2. External Anatomy 



41. Spinal nerves of fetal pig. In a fetal pig of 8 or 10 cm. 

 dissect the spinal cord and nerves. First eviscerate the fetus 

 through a median ventral incision. In the dorsal wall of the 

 abdomen note the spinal nerves segmentally arranged and pass- 

 ing out from the midline of the body. Find the sympathetic 

 trunk and its ganglia extending along either side of the ver- 

 tebral column. Trace the communicating branches (rami 

 communicantes) by slight dissection from the sympathetic gan- 

 glia into the body wall to their connections with the spinal 

 nerves. Note nerves radiating from the sympathetic ganglia, 

 many of which go to form the aortic plexus; others cross the 

 vertebral column and connect with ganglia of the opposite side, 

 while still others pass to more distal sympathetic ganglia (cf. 

 Section 69). 



Draw the dissection at this stage, showing two or three spinal 

 nerves in position and their connections with the sympathetic 

 ganglia and with the related peripheral nerves. 



42. Spinal cord of fetal pig. Now place the fetus on the 

 abdomen with the limbs extended. Make an incision in the 

 dorsal midline along the entire length of the body and remove 

 the muscles and other soft parts adjacent to the vertebral 

 column, working laterally from the midline. Then with bone 

 forceps or strong scissors expose the spinal cord by clipping the 

 neural arches of the vertebrae as close to the intervertebral for- 

 amina as possible. Take care to avoid crushing or otherwise 

 injuring the structures lying in the vertebral canal. Examine 

 the meninges of the spinal cord; then expose the cord and dis- 



