A FROG 177 



each of which one or more short branches run to a spinal 

 nerve. Find these nerves and their ganglia. 



The first, second, and third of these ganglia lie close to the 

 first, second, ^nd third spinal nerves and are joined with them by 

 short branches. The fourth to the ninth sympathetic ganglia, 

 inclusive, are situated nearer the median plane than the first 

 three ; they, together with the longitudinal nerve, lie alongside the 

 dorsal aorta, which will be noticed as a median, dark-colored tube. 

 The fourth sympathetic ganglion is the smallest ; the ninth is 

 the largest and is joined with the ninth spinal nerve by several 

 branches ; the tenth is small and is often wanting. 



Branches from the sympathetic nerves and their ganglia pass 

 to the various viscera. The largest of these branches proceed 

 from the fourth, fifth, and sixth ganglia, and after joining to- 

 gether form a large nerve, called the splanchnic nerve, which 

 supplies the intestine and other viscera. 



Study the sympathetic system; first find the longitudinal 

 nerves and ganglia, and then observe their relations to the spinal 

 nerves and ganglia. 



Exercise 10. Make a semidiagrammatic drawing of the spinal nerves 

 and the sympathetic system. Draw first an outline of the spinal 

 column as it appears in the ventral aspect of the opened body 

 cavity ; number the vertebrae ; draw the spinal nerves and then 

 the sympathetic system. 



The Brain and the Spinal Cord. In order to expose these organs 

 remove the skin and muscles from the back of the head and 

 trunk. Find the juncture of the skull with the backbone. By 

 bending the head slightly down, a space about an eighth of an 

 inch long, which is covered by a dark-colored membrane, may be 

 made to appear between the skull and the backbone. Introduce 

 one blade of the scissors into the skull through the opening, and 

 make a cut along the side of the skull between the eyes. Make a 

 similar cut along the other side, and with the forceps lift off the 

 roof of the skull, thus exposing the brain. Similarly cut through 

 the two sides of the neural canal, which contains the spinal cord, 

 and expose it. 



