THE NERVOUS SYSTEM 105 



sheet which will be observed in front of the corpora quad- 

 rigemina when the hemispheres are pressed apart. 



The paraflocculus projects laterally from the lateral lobe 

 of the cerebellum. Cautiously remove the petrotympanic 

 bone, a bit at a time, and note that the paraflocculus occu- 

 pies the floccular fossa (see the petrotympanic bone). The 

 paraflocculus resembles a toadstool, the enlarged distal end 

 lying in the fossa. The flattened floccus proper is antero- 

 ventral to, and in contact with, the paraflocculus. 



Exercise XXVII. Sketch the dorsal view of the brain. 



Remove the brain from the skull, being careful to pre- 

 serve the roots of the cranial nerves. Care should be taken 

 to keep the paraflocculus intact. The connections between 

 the cranial nerves and the brain are easily broken. If 

 considerable care is used in dissecting away the bone 

 around the foramina of the nerves, many of them may 

 be removed almost entire on that side of the head where 

 the muscles were taken away. Separate the brain from 

 the spinal cord and immerse it in a weak formalin solu- 

 tion, where it may be studied. 



Each olfactory lobe will now be seen to contain two 

 parts — the olfactory hulh, and the olfactory trmt. Each 

 bulb is a swelling at the anterior end of the tract, and in 

 a preserved specimen the former is considerably darker 

 than the latter. The tract rests in a depression on the 

 oblique anterior surface of the cerebral hemisphere. By 

 its distinct whiteness each tract may be followed backward 

 and outward to the level of the optic chia^ma, where it dis- 

 appears. Two pear-shaped areas darker than the olfac- 

 tory tracts extend from the olfactory lobes back to the 

 optic chiasma. They meet in the median plane, and each 

 is limited laterally by the olfactory tract. 



The optic nerves of mammals cross at the optic cMasma, 



