A TRACTUS OLFACTO-TEGMENTALIS IN THE HUMAN 
FETAL BRAIN! 
J. B. JOHNSTON 
University of Minnesota 
NINE FIGURES 
It is commonly taught that the most direct pathways over 
which impulses aroused in the olfactory centers may reach the 
motor centers are the two following: 
a. From the olfactory centers in the forebrain to the tuber 
cinereum or the corpus mammillare, and from these to the teg- 
mentum or possibly to motor centers directly; 
b. From the forebrain centers to the nucleus habenulae, thence 
over the bundle of Meynert to the interpeduncular nucleus and 
thence to motor centers over paths not well known. 
The following description adds to the evidence that a con- 
nection exists between the olfactory and lower centers without 
interruption in the diencephalon. 
The brain studied is that of a fetus 145 mm. in length, crown- 
rump measurement. It was received fresh and fixed in 15 per 
cent formalin. Sections were cut transverse to the long axis 
- of the hemispheres and lengthwise of the brain stem, 50 microns 
in thickness, and stained with Delafield’s hematoxylin. The 
preservation proved to be excellent. | 
The brain at this age is largely composed of cell-masses which 
are deeply stained. The fibers take little stain and where defi- 
nite bundles are present, these stand out sharply among the 
cell-masses and neuropile. Certain well known tracts, such as 
the bundles entering into the anterior commissure and the for- 
nix, are very clearly defined in this brain. . 
In a section passing just rostral to the anterior commissure 
(fig. 4) we see on the right side the precomntissural fibers of the 
1 Neurological Studies, University of Minnesota, No. 20, April 1, 1915. 
283 
