90 LABORATORY OUTLINE OF NEUROLOGY 



9. Optional Dissections of the Brain Stem 



102. The dissections described in the preceding pages can 

 be performed upon either sheep or human brains, even though 

 the latter be not very well preserved. In the following pages 

 (Sections 103 to 111) directions are given for a more complete 

 dissection of some of the structures of the human brain stem 

 than it is practicable to carry out upon the sheep's brain, and 

 for these dissections well-preserved human brains which have 

 been hardened in formalin are necessary. All of these dis- 

 sections can be performed on one lateral half of the human 

 brain, save that the connections of the cerebellar peduncles 

 (Sections 103 to 105) within the cerebellum cannot easily be 

 demonstrated in case the cerebellum has previously been 

 removed as described in Section 49. 



These dissections, being in some cases more difficult than 

 those previously described, can best be done as a review exercise 

 after completion of the preceding exercises. Upon completion 

 of the dissection of Sections 103 to 111 preserve the specimen 

 for later use (Sections 141 to 151). 



103. Corpus restiforme. — Upon lifting up the posterior border 

 of the cerebellum a strong band of fibers is seen leaving the 

 posterior part of the cerebellar peduncle complex to turn back- 

 ward along the dorso-lateral border of the oblongata. This, 

 the corpus restiforme, is crossed immediately behind the 

 cerebellum by the dorsal root and nucleus of the VIII nerve 

 (tuberculum aeusticum). Cut through this cochlear VIII 

 root and reflect its fibers so as to expose the dorsal aspect of 

 the corpus restiforme, but do not remove the VIII root and 

 nucleus. Locate the vestibular (ventral) root of the VIII 

 nerve. Its fibers pass under the corpus restiforme to enter the 

 vestibular nucleus in the floor of the fourth ventricle medi- 

 ally of the corpus restiforme. Vestibular VIII root fibers pass 

 from the vestibular root into the corpus restiforme and also 

 other fibers of the second order from the vestibular nucleus to 

 its medial border; but their dissection should not be attempted 

 at this time. Trace the restiform body backward and note that 

 it receives external arcuate fibers from the somatic sensory 

 region of the opposite side. At the level of the inferior olive 



