36 GENERAL BIOLOGY 



A swelling in the region of the arm would constitute a 



brachial enlargement, and one near the legs a sacral 



or lumbar enlargement. How does the cord terminate ? 



Make a large drawing of the brain and spinal cord from 



the dorsal side. Use care in getting the dimensions and 



proportions accurate, measuring the parts with a rule if 



necessary. 



Carefully remove the brain and cord from the body, 



place in a watch glass of water, and construct an accurate 



drawing of the ventral side of the brain. In addition to 



the parts already observed the following should be identified: 



(h) Optic Chiasma. Formed by the crossing of the optic 



nerves as they leave the optic lobes. 

 (i) Infundibulum. A small shield-shaped body posterior 



to the optic chiasma. 



(j) Pituitary Body. This lies in a little pocket of bone in 

 the floor of the skull. It is usually torn from its 

 attachment to the infundibulum when the brain is 

 removed from the cranial cavity. 



2. The Sympathetic System. This is best seen by placing 

 the animal ventral side up, moving the viscera to one side 

 and looking for a very delicate thread-like nerve, the sym- 

 pathetic nerve, which runs along one side of the dorsal aorta; 

 a similar nerve is present in the same position on the other 

 side. When these are found the organs of the body and the 

 lower jaw should be removed, but the dorsal aorta left in 

 place. Place the animal under water and lift the dorsal 

 aorta to find the sympathetic nerves, their ganglia and con- 

 nections with the spinal nerves. Observe carefully the 

 relation of sympathetic and spinal nerves, the position and 

 number of sympathetic ganglia, and the delicate nerves con- 

 necting spinal and sympathetic nerves. 



A single drawing should be made to show the sympathetic 

 and peripheral systems. 



