396 



DISSECTION OF THE RABBIT. 



c. The mid-brain, or mesencephalon. 



i. The corpora guadrigemina, or optic lobes, form 

 the dorsal portion of the mid-brain, and are 

 now well seen. 



ii. The crura cerebri form the base of the mid- 

 brain : after removal of the optic tracts they 

 can be traced forwards and outwards from 

 the anterior border of the pons Varolii to the 

 optic thalami. 



Fig. 70. Lepus cuniculus. Transverse section of the brain, passing 

 through the middle commissure of the third ventricle. The shading 

 indicates diagrammatically the distribution of white and grey 

 matter. The section is taken somewhat obliquely, so as to show 

 different parts on the two sides, (a. m. m.) 



A, optic thalamus, forming the side-wall of the third ventricle. B, part ol 

 the third ventricle above the middle commissure. C, middle commissure. D, 

 infundibulum. E, corpus callosum. F, temporal lobe of the left cerebral hemi- 

 sphere. G, descending cornu of the right lateral ventricle. H, hippocampus 

 major. 



2. Longitudinal section of the brain. 



Divide the brain into right and left halves by a median 

 longitudinal section. Place the left half in a small dish of 

 spirit, and examine its inner surface. 



If the dissection has been properly performed, the left half 



