XIII.] THE FROG. 231 



the nasal chamlDer, give off a number of branches 

 which are distributed on that membrane. 



b. The thalamencephalon : lying between the poste- 

 rior ends of the cerebral hemispheres : on it are 

 to be noticed — 



a. The pineal gland: a very small mass in front; 

 not composed of nervous tissue. 



/3. The thalami optid: the nervous masses seen 

 below the pineal gland: between them lies a 

 narrow cavity, the third ventricle, 



c. The optic lobes {mesencephalon) : a pair of rounded 

 eminences lying behind the thalamencephalon. 



d. The cerebellum (metencephalon) : a narrow trans- 

 verse band lying behind the optic lobes. 



e. The medulla oblongata (myeloncephalon) : the 

 portion of the brain lying behind the cerebellum. 



a. Lying on the medulla oblongata is a triangular 

 depression (4th ventricle) with its apex turned 

 backwards. 



3. The spinal cord. 



a. Its form : wide in front, but narrowing rapidly 

 about the 5th or 6th vertebra, and thence con- 

 tinued along the neural canal as a slender taper- 

 ing filament. 



b. The groove {posterior fissure) running along its 

 middle line. 



c. The spinal nerves arising from it. 

 a. Ten on each side. 



