44 LABORATORY OUTLINE OF NEUROLOGY 



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 depend- 

 encies. 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 com- 

 municantes) by slight dissection from the sympathetic ganglia 

 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 vertebra? 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 dissect 

 several spinal nerves of one side sufficiently to show the spinal 

 ganglia and the adjoining portions of the spinal nerve trunks. 



43. Make a transverse section through the fetus in the tho- 



