868 NEUROLOGY 





receive impulses from the mitral cells. Thess fibers of the medullary stria end for 

 the most part in the habenular nucleus of the same side, some, however, cross in the 

 habenular commissure (dorsal part of the posterior commissure) to the habenular 

 nucleus of the opposite side. A few fibers of the medullary stria are said to pass 

 by the habenular nucleus to the roof of the mid-brain, especially the superior col- 

 liculus, while a few others come into relation with the posterior longitudinal bundle 

 and association tracts of the mesencephalon. 



The ganglion of the habenulae located in the trigonum habenulse just in front of 

 the superior colliculus contains a mesial nucleus with small cells and a lateral 

 nucleus with larger cells. The axons of these cells are grouped together in a bundle, 

 the fasciculus retroflexus of Meynert, which passes ventrally medial to the red 

 nucleus and terminates in a small medial ganglion in the substantia perforata 

 posterior, immediately in front of the pons, called the interpeduncular ganglion. 



The interpeduncular ganglion has rather large nerve cells whose axons curve 

 backward and downward as the tegmental bundle of Gudden, to end partly in the 

 dorsal tegmental nucleus and surrounding gray substance where they come into 

 relation with association neurons and the dorsal longitudinal bundle of Schiitz. 



The majority of the axons that arise from the mitral cells of the olfactory bulb 

 and course in the olfactory tract course in the lateral olfactory stria to the uncus 

 and hippocampal gyrus, and terminate in the cortex. Other fibers probably pass 

 to the uncus and hippocampal gyrus from the primary olfactory centers in the 

 trigonum and anterior perforated substance. The gyrus hippocampus is continued 

 through the isthmus into the gyrus cinguli which passes over the corpus callosum to 

 the area parolfactoria. The cortical portions of these gyri are connected together 

 by a thick association bundle, the cingulum, that lies buried in the depth of the 

 gyrus cinguli extending forward to the parolfactory area and backward into the 

 hippocampal region. The axons from the gyrus cinguli pass into the cingulum, 

 many of them bifurcate, the anterior branches together with the axons which run 

 in that direction are traceable as far forward as the anterior part of the septum 

 pellucidum and the anterior end of the corpus striatum, where some of them are 

 incorporated with projection fibers passing toward the internal capsule. The 

 branches and axons which pass backward terminate partly in the hippocampus, 

 the dentate gyrus and hippocampal gyrus. Shorter association fibers connect 

 various sections of the gyrus fornicatus (cingulate gyrus, isthmus, and hippocampal 

 gyrus) and these with other regions of the cortex. These gyri constitute the cortical 

 center for smell. 



The dentate gyrus which may be considered as a modified part of the hippo- 

 campus is partially separated from the gyrus hippocampus by the hippocampal fis- 

 sure and from the fimbria by the fimbrio-dentate sulcus; it is intimately connected 

 with the hippocampal gyrus and the hippocampus. When followed backward the 

 dentate gyrus separates from the fimbria at the splenium, loses its incisions and 

 knobs, and as the fasciola cinerea passes over the splenium onto the dorsal surface 

 of the corpus callosum and spreads out into a thin layer of gray substance known 

 as the indusium, which can be traced forward around the genu of the corpus 

 callosum into the gyrus subcallosus. The white matter of the indusium known 

 as the medial longitudinal striae (nerves of Lancisi) and the lateral longitudinal striae, 

 are related to the indusium somewhat as the cingulum is to the gyrus cinguli. 

 Axons from the indusium pass into the longitudinal striae, some running forward 

 and others backward while some after entering the medial longitudinal stria, pierce 

 the corpus callosum to join the fornix. Some of the fibers which pass forward 

 extend around the front of the corpus callosum and the anterior commissure, then 

 curve downward, according to Cajal, to enter the corpus striatum where they join 

 the olfactory projection-path. Other fibers are said to arise in the parolfactory 

 area, the gyrus subcallosus and the anterior perforated substance (diagonal band of 



