108 GENERAL BIOLOGY. 



the cerebral hemispheres. In the middle 

 line between the diverging ends of the 

 cerebral hemispheres the pineal gland 

 is borne. 



(d) The optic lobes: two conspicuous rounded 



bodies, one on each side. 



(e) The cerebellum: a narrow ridge posterior 



to the optic lobes. 



(/) The medulla oblongata: the region posterior 

 to the cerebellum, broadest at the an- 

 terior end and passing gradually into 

 the spinal cord. Its dorsal wall is a 

 thin, highly vascular membrane, the 

 choroid plexus of the fourth ventricle. 

 Beneath the choroid plexus is the cav- 

 ity of the fourth ventricle. 



2. The Spinal Cord : continued posteriorly from 



the medulla oblongata. It is flattened 

 dorso-ventrally. Near the region of the 

 sixth vertebra it tapers rapidly to a slender 

 thread, the filum terminale. The filurn ter- 

 minale and the proximal ends of the lumbar 

 nerves form the cauda equina. Note in the 

 median line a slight groove not well marked 

 throughout, the dorsal fissure. 

 Turn the brain and spinal cord ventral side upper- 

 most, and sketch. Note : 



3. The Brain : 



(a) The olfactory lobes and nerves. 



