74 THE FROG 



dibulum posterior to the chiasma ; posteriorly the infundib- 

 ulum is continuous with the pituitary body or hypophysis 

 which is generally torn off when the brain is removed from 

 the cranium. 







Compare the brain of the frog with figures or a model of 

 the brain of man. What parts are relatively larger in the 

 human brain? 



With a sharp scalpel, razor, or scissors carefully slice off 

 the roof (dorsal wall) of the brain until the cavities are ex- 

 posed throughout its entire extent. In the cerebral hemi- 

 spheres make out a pair of cavities, the first and second 

 ventricles; do they extend into the olfactory lobes? The 

 unpaired cavity (third ventricle) of the thalamencephalon 

 connects in front with the first and second by transverse 

 passages, the foramina of Monro. In the optic lobes are a 

 pair of optic ventricles, which, since they do not occur in 

 mammals, are not numbered. The optic ventricles com- 

 municate with a median cavity, the aqueduct of Sylvius or 

 iter e tertio ad quartum ventriculum, which, as the latter 

 name implies, connects the third ventricle with the fourth 

 ventricle situated in the medulla. 



Study prepared slides showing cross-sections through dif- 

 ferent regions of the brain. With the aid of figures show- 

 ing sagittal and horizontal sections (see Leuckart's chart, 

 or Holmes' Biology of the Frog), determine from what 

 parts of the brain the cross-sections are taken. Make out- 

 line drawings of sections through four different regions, and 

 label all the parts shown. 



2. The peripheral nervous system. Of the cranial 

 nerves, the olfactory and optic nerves were readily observed 

 during the study of the brain. On account of the difficulty 



