A MANUAL OF ZOOLCGY 67 



THE NERVOUS SYSTEM— Cut away the muscles on 

 both sides of the spinal column. Cut off the dorsal portion 

 of the skull and the vertebrae, being careful not to de- 

 stroy the contents of ttie cavities exposed. Notice that the 

 nervous system consists of two parts: the central and the 

 peripheral portions. The central portion consists of the 

 iDrain and the spinal cord. Examine carefully the dorsal 

 surface of the brain. Note the olfactory lobes, the most 

 anterior portion; cerebral hemispheres, immediately pos- 

 terior to the olfactory lobes; the thalamencephalon, poster- 

 ior to the cerebrum and between its diverging ends; the 

 optic lobes, two oval bodies posterior to the former; note 

 the pigment in the pia mater over the optic lobes; the 

 cerebellum, a narrow strip or band posterior to the optic 

 lobes; the oblongata, immediately posterior to the cerebel- 

 lum and continuous with the spinal cord. Locate the chor- 

 oid plexus, a thick membrane covering the thalamencepha- 

 lon. Locate the pineal body. The optic thalmi are the thick- 

 ened sides of thfe thalamencephalon. Slice ofc the top of the 

 brain without removing it from the skull, .thereby exposing 

 several cavities, the ventricles. The most anterior and 

 lateral cavities are the lateral ventricles. What is their 

 extent? The cavity in the thalamencephalon is the third 

 ventricle. Note its connection with the lateral ventricles 

 through the foramina of Monro. Locate the infundibulum 

 and the pineal body. The aqueduct of Sylvius leads from 

 the cavity known as the third ventricle -to the fourth ven- 

 tricle. Notice the cavity in the optic lobes. Cut the me- 

 dulla at the level of the posterior part of the skull and 

 carefully remove the brain, keeping in mind that there 

 are a number of important things on the ventral surface 

 that may be easily destroyed. Find two large nerves that 

 appear to cross, the optic chiasma. Notice a depression 

 just posterior to the optic chiasma, which causes a swell- 

 ing on each side, the tuber cinereum. If the pituitary body 

 has been left in the skull in taking out the brain, the torn 

 end of the infundibulum will be seen in connection with 

 the posterior part of the tuber cinereum. Find the crura 

 cerebri at the base of the optic lobes. Notice a fissure 

 continuous with the ventral fissure of the spinal cord, 

 the ventral fissure of the brain. Is the spinal cord uniform 



