THE NERVOUS SYSTEM 



In an earlier study it has Ix'en dcinonstrated that the con- 

 traction of muscles when properly attached to skeletal elements 

 may cause parts to move. Before a muscle contracts it receives a 

 nervous stimulus from a controlling; center, and before compli- 

 cated and beneficial movements take place these muscular 

 contractions must be coordinated. If an animal is to acquire 

 any degree of intelligence it must be able to accumulate experi- 

 ences. These may be taken as the general services provided by 

 the nervous system. 



This communicating, coordinating, and controlling system 

 in animals like the frog and man comprises two divisions: (1) 

 the central nervous system, formed by the brain and spinal cord; 

 (2) the peripheral nervous system, comprising the nerves which 

 extend between the central system and the periphery of the body 

 (or outlying organs). Specimens for this study have been pre- 

 pared so as to soften the bones which maybe cut with instruments. 



If the skin has not already been removed from the animal 

 clip off that of the dorsum. Remove a narrow strip of muscle 

 from the middorsal region beginning at the cranium and extend- 

 ing to the sacral vertebra. Expose the brain and spinal cord 

 by carefully snipping away the roof of the skull and vertebral 

 column with the aid of scalpel, forceps, and scissors. Begin 

 by cutting through the cartilage just caudad of the external 

 nares from this point work caudad slicing off the dorsal portion 

 of the cranium and vertebral column until the outlines of the 

 brain and spinal cord are exposed to view. Care must be used 

 to avoid cutting or injuring the soft nervous tissues while remov- 

 ing the roof of the skull and vertebral column and to avoid injury 

 to the nerves leaving any part of the central system. Do not 

 cut away too much of the neural arches of the vertebra). In 

 removing pieces of .skeletal material from the sides of the central 

 nervous system always cut away from the middorsal line. When 

 the central nervous system is clearly exposed identify the parts 

 to be seen from the dorsal aspect. 



Dorsal Aspect of the Brain.— Observe the pigmented membrane 

 closely applied to the nervous tissue. This membrane is called 



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