THE MAMMALIAN NERVOUS SYSTEM 111 



11. Optional Dissections of the Cerebrum 



141. The association tracts. — The same specimen upon which 

 the dissections outlined in Sections 102 to 111 were made can be 

 used for the following dissections of the cerebrum. The associa- 

 tion tracts can be dissected out in great detail, following the pro- 

 cedure directed for the sheep and human in Sections 119 and 

 120, working carefully with text-book diagrams and descriptions 

 of the chief systems in mind and teasing off the more superficial 

 systems before attempting to study the deeper systems. It 

 will be found that the stronger and more easily isolated asso- 

 ciation tracts do not connect the projection centers, but the 

 association centers. In view of the fact that in the sheep the 

 association centers are small when compared with man, the 

 greater ease with which the human association tracts can be 

 isolated by dissection finds its obvious explanation. 



142. The olfactory apparatus. — Examine the human olfactory 

 bulb and strise and compare them with those of the sheep. Dis- 

 sect the olfactory tracts in the way directed for the sheep brain 

 in Sections 123 to 126; but do not continue the dissection as di- 

 rected in Section 127. In this dissection expose the hippocampus 

 as follows: Lay the specimen down on its median surface and 

 carefully tease off the fibers of the inferior longitudinal fasciculus 

 from the lateral convex surface of the temporal lobe until the 

 inferior horn of the lateral ventricle is opened. The teasing 

 should stop at this point. Now with a probe trace the inferior 

 horn of the lateral ventricle to the anterior end of the temporal 

 lobe and follow the probe with a scalpel cut, thus opening up the 

 inferior horn of the lateral ventricle. Similarly probe from the 

 posterior border of the incision just made backward toward the 

 occipital pole of the hemisphere and follow the probe with a 

 scalpel cut, thus opening the posterior horn of the ventricle in 

 the occipital lobe. Now pull apart the walls of the lateral 

 ventricle as thus opened and locate the hippocampus, a rounded 

 eminence in the floor of the inferior horn of the ventricle. At 

 the point where the inferior and posterior horns of the ventricle 

 join, the hippocampus will be seen to turn sharply medialward. 

 With a scalpel follow the lateral and posterior borders of the 

 hippocampus with a clean cut. This incision must be made 



