302 COORDINATION AND SENSATION 



should be killed with chloroform and secured to a board as in the dis- 

 section of the abdomen (page 169). Open the abdominal cavity and 

 remove the contents, tying the alimentary canal where it is cut, and 

 washing out any blood which may escape. Dissect for the nervous 

 system in the following order : 



1. Cut away the front of the chest, exposing the heart and lungs. 

 Find on each side of the heart a nerve which passes by the side of the 

 pericardium to the diaphragm. These nerves assist in controlling 

 respiration and are called the phrenic nerves. Find other nerves going 

 to different parts of the thorax. 



2. Remove the heart and lungs. Find in the back part of the 

 thoracic cavity, on each side of the spinal column, a number of small 

 " knots " of nervous matter joined together by a single nerve. These 

 are sympathetic ganglia. Where the neck joins the thorax, find two 

 sympathetic ganglia much larger than the others. 



3. Cut away the skin from the shoulder and upper side of the fore 

 leg. By separating the muscles and connective tissue where the leg 

 joins the thorax, find several nerves of considerable size. These con- 

 nect with each other, forming a network called the brachial plexus. 

 From here nerves pass to the thorax and to the fore leg. 



4. From the brachial plexus trace out the nerves which pass to 

 different parts of the fore leg. In doing this separate the muscles with 

 the fingers and use the knife only where it is necessary to expose the 

 nerves. Note that some of the branches pass into the muscles, while 

 others connect with the skin. 



5. Remove the skin from the upper portion of one of the hind legs 

 and separate the muscles carefully until a large nerve is found. This 

 is one of the divisions of the sciatic nerve. Carefully trace it to the 

 spinal cord, cutting away the -bone where necessary, and find the con- 

 nections of its branches with the cord. Then trace it toward the foot, 

 discovering its branches to different muscles and to the skin. 



6. Unjoint the neck and remove the head. Examine the spinal cord 

 where exposed. Cut away the bone sufficiently to show the connection 

 between the cord and one of the spinal nerves. On the dorsal root 

 of one of the nerves find a small ganglion. What is it called? 



7. Fasten the head to a small board and remove the scalp. Saw 

 through the skull bones in several directions. Pry off the small pieces 

 of bones, exposing the upper surface of the brain. Study its mem- 

 branes, convolutions, and divisions. 



