THE MAMMALIAN NERVOUS SYSTEM 107 



ity of the anterior commissure with the amygdala under the 

 uncus, running dorsally of the internal capsule fibers at the line 

 of contact of the thalamus with the cerebral hemisphere. The 

 dissection of this tract should not be made at this time; see 

 Section 132. 



(6) Diagonal band of Broca. This is a ridge extending 

 transversely across the ventral aspect of the cerebral hemi- 

 sphere between the area olfactoria intermedia, or tuberculum 

 olfactorium, and the optic chiasma (Fig: 8). It contains both 

 cells and fibers, the latter connecting the medial olfactory area 

 with the lateral olfactory area. The diagonal band and the 

 stria terminalis contain correlation fibers connecting the same 

 areas, the former running across the extreme ventral surface of 

 the hemisphere and the latter across the extreme dorsal surface 

 of the brain stem along the line of contact of the cerebral 

 hemisphere with the thalamus. 



(7) Tractus mamillo-thalamicus (tract of Vicq d'Azyr or 

 tractus thalamo-nlamillaris) . This tract runs from the cor- 

 pus mamillare forward and dorsalward to the nucleus ante- 

 rior of the thalamus. It can readily be dissected by scraping off 

 the ependyma of the third ventricle, beginning in the region of 

 the mammillary body. 



(8) Tractus mamillo-tegmentalis. By very slight dissection, 

 beginning in the median plane, this tract can be exposed. It 

 runs from the mammillary body dorsalward and spinalward 

 through the tegmental region under the aqueduct of Sylvius. 



(9) Tractus mamillo-peduncularis. This tract arises with 

 the last and runs somewhat farther ventrally in the cerebral 

 peduncle. 



(10) Tractus habenulo-peduncularis (fasciculus retroflexus, 

 or Meynert's bundle) . This tract also can readily be dissected. 

 It runs from the habenula into the ventral part of the cerebral 

 peduncle immediately behind the mammillary body, crossing 

 the tractus mamillo-tegmentalis at a somewhat deeper level 

 (more laterally). 



The three tracts last mentioned carry olfactory nervous 

 impulses into the motor centers of the cerebral peduncle. 

 After synapses here the pathways are continued to the lower 

 motor centers. 



